Add link to comparison from system note, update changelog

## What does this MR do?
Adds a link to the comparison between the previous and latest version.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

## Screenshots (if relevant)

![Screen_Shot_2016-10-01_at_3.37.03_AM](/uploads/89b48dc1b2ed868cf5dd85300e6b37a0/Screen_Shot_2016-10-01_at_3.37.03_AM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [ ] ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #22773

See merge request !6607

Link to the "What requires downtime?" page from the Migration Style Guide

## What does this MR do?

Adds a link from migration style guide -> "What requires downtime?"

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

The two pages really need to be read together, so having the link is helpful.

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

See merge request !6636

[ci skip]

Add word-wrap to issue title on issue and milestone boards

## What does this MR do?
Adds word-wrap to the issue title found on the issue board and the milestone boards

## Are there points in the code the reviewer needs to double check?
Shouldn't be

## Why was this MR needed?
Improves UI

## Screenshots (if relevant)
Before:
![Screen_Shot_2016-09-19_at_10.19.18_AM](/uploads/7b79fe87c12c0d9a89fff5c725c546a4/Screen_Shot_2016-09-19_at_10.19.18_AM.png)
![Screen_Shot_2016-09-19_at_10.19.14_AM](/uploads/80a7e37433c98a406806249f01fe72fd/Screen_Shot_2016-09-19_at_10.19.14_AM.png)


After:
![Screen_Shot_2016-09-19_at_10.18.54_AM](/uploads/e3a9420262a5d521478bea5601afafab/Screen_Shot_2016-09-19_at_10.18.54_AM.png)
![Screen_Shot_2016-09-19_at_10.19.04_AM](/uploads/b87d661bd1492777c4f677ea3ed09dcc/Screen_Shot_2016-09-19_at_10.19.04_AM.png)


## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #22274

See merge request !6412

Merge branch 'jimmykarily/gitlab-ce-notify_current_user_when_merging_an_mr_after_build_succeeds' into 'master'

Notify current_user about automatic merge after successful build

It enables notifications to the initiator of a merge when the MR is flagged as "Merge when build succeeds".

Because when running Builds, quite some time passes between the user's
action and the actual Merge so it is a good thing to notify the
initiator of the Merge when it actually happens.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14409

See merge request !6534

Merge branch '21983-member-add_user-doesn-t-detect-existing-members-that-have-requested-access' into 'master'

Resolve "`Member.add_user`doesn't detect existing members that have requested access"

## What does this MR do?

This merge request handle the case when an access requester is added to a group or project (via the members page or the API).

In `Member.add_user`, if an access requester already exists, we simply accept their request (and set the `created_by`, `access_level` and `expires_at` attributes if given).

## Are there points in the code the reviewer needs to double check?

I've taken the opportunity to cleanup the whole `{Group,Project}Member.add_user*` methods since it was quite a mess.

## What are the relevant issue numbers?

Closes #21983

See merge request !6393

New `Members::RequestAccessService`

Part of #21979.

See merge request !6265

Preserve label filters when sorting

## What does this MR do?

Allows Issues that are already filtered by labels to be sorted without losing the label filters.

## Why was this MR needed?

Users don't expect to lose their label filters when sorting Issues.

## What are the relevant issue numbers?

Closes #20982

See merge request !6136

Center the header logo

_Originally opened at !6507 by @AshleyDumaine._

- - -

## What does this MR do?

* Centers the header logo using `relative` positioning on the svg or img in the header-logo

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

The custom wide header logos aren't centered after logging in as seen in #22494

## Screenshots (if relevant)

| Before | After |
| --------- | ------ |
| ![Screen_Shot_2016-09-24_at_3.35.26_PM](/uploads/576db77e0eb299b06d2a5abf341f058f/Screen_Shot_2016-09-24_at_3.35.26_PM.png) | ![Screen_Shot_2016-09-24_at_3.35.51_PM](/uploads/47237b6c28d438a6f255dffb8b3d39d4/Screen_Shot_2016-09-24_at_3.35.51_PM.png) |

Signout (for centering comparison):
![Screen_Shot_2016-09-24_at_3.35.59_PM](/uploads/4484313ff5841774769c4737584af7fc/Screen_Shot_2016-09-24_at_3.35.59_PM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #22494

See merge request !6610

Changed zero padded days to no padded days in date_format

## What does this MR do?
Changed zero padded days to no padded days in date_format so that calendar spec tests will pass.

Specs were failing because it was looking for `Saturday Oct 01, 2016` when it should have been looking for `Saturday Oct 1, 2016`

## Are there points in the code the reviewer needs to double check?
None

## Why was this MR needed?
Fixes failing test

## Screenshots (if relevant)
None

## Does this MR meet the acceptance criteria?

- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #22861

See merge request !6634

Changed compare dropdowns to dropdowns with search input

## What does this MR do?

This changes the compare dropdowns from text inputs, that when clicked, open a dropdown of branches/tags to dropdowns that have a dropdown toggle and an isolated search input.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

This was needed to fix the poor UX highlighted in #22221, where opening the dropdown showed an initially filtered set of results because the dropdown toggle was the dropdown filter itself. The compare page is always loaded with `master` as each branch/tag selection, so when opening the dropdown, it would only show results matching `master`.

## Screenshots (if relevant)

![2016-09-27_18.28.10](/uploads/0ea1d91cb592c6e140ed62c336e77227/2016-09-27_18.28.10.gif)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?


Closes #22221

See merge request !6550

MR banner & flash notices updates

### What does this MR do?
* Moves the create MR banner below subnav
* Changes MR banner background to white
* Moves flash notices underneath subnav
* Adds container within flash notices to align with content

Closes #22767 
### Why was this MR needed?
It looked a bit out of place between the two navs & had unneeded spacing.

### Screenshots (if relevant)
Before:   
<img src="/uploads/c1676a1923893a7ba7e1c6d6a50d4ea6/Screen_Shot_2016-09-09_at_7.17.31_PM.png" width="800px">
After:   
<img src="/uploads/74a2d6c8c43b9a15cd535a2a7adb2685/Screen_Shot_2016-09-28_at_3.41.29_PM.png" width="800px">

Before:   
<img src="/uploads/285e3de31326c48de43bb48abd4d907c/Screen_Shot_2016-09-29_at_10.57.55_AM.png" width="800px">
After:    
<img src="/uploads/0877e3e45755e5ca36694c52ad2e6198/Screen_Shot_2016-09-29_at_10.56.04_AM.png" width="800px">

With both alert and broadcast message:
![Screen_Shot_2016-09-29_at_11.06.51_AM](/uploads/ba3963a73b5c82940533c369ec54ec50/Screen_Shot_2016-09-29_at_11.06.51_AM.png)


See merge request !6581

Add Frontend Development Guidelines to the Developer Documentation

## What does this MR do?

WIP incomplete draft of some Frontend Development Guidelines for contributors to the project, new hires, and for other projects and persons to look to for guidance.

These are all subject to removal, modification, etc. If you disagree with any of these, please feel free to voice your concerns :)

## Why was this MR needed?

There are a number of guidelines we currently follow implicitly, this makes them more official and available for reference/discussion.

It also exists as a reference for certain patterns we use which may be unfamiliar to new contributors, e.g. the per-page JS.

Feel free to give feedback on wording, missing sections/guidelines, whether a guideline should even exist, etc.

See merge request !5477

Updated diff toggle targets and added icon

## What does this MR do?

Adds the new diff toggle icon and alters the toggle targets.

User can now click on the file header bar _(where no other elements are above it, apart from the icon)_ and the `Click to expand` link to expand the diff and no where else.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

## Screenshots (if relevant)

![Screen_Shot_2016-09-02_at_15.35.15](/uploads/c1cb8c0547328153250294d6c95dd96a/Screen_Shot_2016-09-02_at_15.35.15.png)

####  Gif

![2016-09-02_15.34.31](/uploads/abaefaeba9ce8ef129522dae34574c57/2016-09-02_15.34.31.gif)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #21369 

Closes #20326

See merge request !6183

Add a spec to verify comparison context inclusion in path when a version is chosen to compare against

Added soft wrap option to editor (attempt 2 after killing master)

Previously !6188.

## What does this MR do?

Adds a `Soft wrap` button to the editor, when clicked, it wraps the text in the editor and changes to `No wrap`, then when clicked, it unwraps the text in the editor.

## Are there points in the code the reviewer needs to double check?

Let's make sure we dont blow up `master` this time. 😨 😆 

## Why was this MR needed?

## Screenshots (if relevant)

https://youtu.be/8LW5nQsraSM

#### No wrap

![Screen_Shot_2016-09-02_at_19.54.54](/uploads/97f2d1b2d415d03fe1b0be0640ab12e0/Screen_Shot_2016-09-02_at_19.54.54.png)

#### Soft wrap

![Screen_Shot_2016-09-02_at_19.54.45](/uploads/5af425587ce7198e015cce58440971b9/Screen_Shot_2016-09-02_at_19.54.45.png)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?


Closes #18297

See merge request !6594

Closes #20982

https://gitlab.com/gitlab-org/gitlab-ce/issues/20982

Updated tests

Added tests

Added awesomeeeeee icons

Signed-off-by: Rémy Coutable <remy@rymai.me>

Fix lint-doc error

## What does this MR do?
Removes duplicate changelog versions to fix lint-doc error (https://gitlab.com/gitlab-org/gitlab-ce/builds/4621603)

See merge request !6623

Add missing values to linter (`only`, `except`) and add new one `Environment`

Closes #21744 

See merge request !6276

Before rendering `show` template we close open merge request without source project. This way there is no need to render `invalid` template. I think that it's better solution than !6383

See merge request !6478

Update "Installation from source" guide for 8.13.0

Following the steps from https://gitlab.com/gitlab-org/release-tools/blob/master/doc/release-candidates.md#creating-rc1.

See merge request !6565

Added "View wiki pages" to list of actions granted to various user permission levels in a project.

This MR clarifies the actions allowed by various user permission levels in a project to include "View wiki pages"

See merge request !5749

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>