Add Discussion model to represent MR/diff discussion

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/10325.

See merge request !5376

UI bug fixes

Closes #20074   
Closes #20094 

Regression UI bug fixes
* Fix broken status icon on project page
* Center tooltip on empty state in pipeline
* Reduce max-width of commit title in pipeline so more fits in table
* Fixes firefox rendering (icons getting cut off)
* Fixes Safari rendering of SHA icon

See merge request !5383

Bump vmstat version to fix issues reporting on FreeBSD

Minor changes from 2.1.0 to 2.1.1:

https://github.com/threez/ruby-vmstat/commits/master

See merge request !5405

Don't drop in DropAndReaddHasExternalWikiInProjects

## What does this MR do?

This MR fixes the migration in question so it doesn't first drop and then re-add a column.

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

Not really.

## Why was this MR needed?

The old migration could lead to application errors as the column would temporarily not exist between the drop column and add column statements.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-com/infrastructure/issues/239

## Does this MR meet the acceptance criteria?

- [x] ~~[CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added~~
- [x] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [x] 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)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5402

Add allow_failure CI documentation

## What does this MR do?

Adds documentation for the `allow_failure` keyword for the CI.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/17669

See merge request !5398

Dropping a column and then re-adding it can lead to the application
throwing errors as the column may temporarily not exist. To work around
this we'll reset the various project rows in batches _without_ removing
any columns.

Don't use `params[:id]` while building `markdown_preview_path`.

- Closes #20079

See merge request !5400

1. Instead, use `@page.title`, since it's always guaranteed to be around
   in a wiki.

2. `params[:id]` is _not_ always guaranteed to be around - if a page is
    created with errors, `render :edit` is called, and `params[:id]` is
    `nil`.

3. More context: https://gitlab.com/gitlab-org/gitlab-ce/issues/20079#note_13223240

Fix migration to make it fast

## What does this MR do?

Changing the migration introduced in !5387 so that it's fast. The idea is that the content of the `projects.has_external_wiki` is currently wrong, so we can just drop and recreate the column.

## Does this MR meet the acceptance criteria?

- [x] No CHANGELOG needed
- Tests
  - [ ] All builds are passing
- [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)

See merge request !5394

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

Cast duration to integer in `TimeHelper#time_interval_in_words`

Fixes #20055.

- [x] No CHANGELOG since it fixes a regression introduced in RC12.
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [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)

See merge request !5391

Fix emails on push for new and deleted branches

## What does this MR do?

Fix EmailsOnPushWorker when the push is either a new branch or a deleted branch.

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

Don't think so.

## Why was this MR needed? / What are the relevant issue numbers?

Closes #20061.

## Does this MR meet the acceptance criteria?

- ~~[CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added~~ (regression)
- ~~[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 [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)


See merge request !5390

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

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

Show tooltip on GitLab export link in new project page

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/19993

When the project path/name is not filled, we should show a tooltip in the `GitLab export` link, plus a flash message if the user still tries to click on it.

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] 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)

See merge request !5363

Hide project name in project activities

## What does this MR do?

- hide namespace and project name on project activity page

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

- did `.event_label` have any meaning?

## Why was this MR needed?

- all events on project activity page are from the same project, so the information was redundant

## What are the relevant issue numbers?

closes #18963

## Screenshots

### Before

![events-before](/uploads/76336e3f5cb08d4ef984df73c89aa90f/events-before.png)

### After

![events-after](/uploads/4a10718ed32960efc115d7854e5cad68/events-after.png)

![after-john-activity](/uploads/d9d151a829d8d32136525e8eb7ea04ad/after-john-activity.png)


See merge request !5068

Add image border in Markdown preview

## What does this MR do?

- add image border in Markdown preview like it is show after a comment is saved
- fix margin and shade of  `<hr>` in Markdown preview

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

Is `.md` the right class to use?

## Why was this MR needed?

The border was missing.

## What are the relevant issue numbers?

fixes #19652

## Screenshots

### Before

![before](/uploads/683e2af7278c33d29b2a1ae19d1136e3/before.png)

### After

![after](/uploads/07dcee531a5696303cb34b4a88357e8a/after.png)


See merge request !5162

Fixed dropdown enter key when searching

## What does this MR do?

When searching in a dropdown you can now just press the enter key to trigger a click on the first row rather than having to press the down key & then enter.

## What are the relevant issue numbers?

Closes #19741 

See merge request !5231

Update doc for award emoji API

## What does this MR do?

It fixes some docs for the award emoji API.

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

@zj I'm assigning you since you wrote this docs.

## Does this MR meet the acceptance criteria?

~~- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added~~
- [x] [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
- [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)

See merge request !5386

Make Service.external_wikis return only active external wikis

Fixes #20067.

## Does this MR meet the acceptance criteria?

- [x] No CHANGELOG since it fixes a RC12 regression
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [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)

See merge request !5387

Merge branch '20041-gitlab-workhorse-version-should-be-update-to-0-7-8-in-our-documentation' into 'master'

Update gitlab-workhorse version to 0.7.8 in installation and update guides

Closes #20041.

See merge request !5385

API for downloading latest successful build

## What does this MR do?

Implement parts of #4255, particularly the API.

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

I still made it that `ref` could be either branch, tag, or even SHA with:

``` ruby
# ref can't be HEAD, can only be branch/tag name or SHA
scope :latest_successful_for, ->(ref) do
  table = quoted_table_name
  # TODO: Use `where(ref: ref).or(sha: ref)` in Rails 5
  where("#{table}.ref = ? OR #{table}.sha = ?", ref, ref).
    success.order(id: :desc)
end
```

Because the reasons I put in:

* https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5142#note_13165543
* https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5142#note_13165921

But if you still think that it's not good to do it this way, I'll drop it and let's think about the other way to satisfy the requirement specified in https://gitlab.com/gitlab-org/gitlab-ce/issues/4255#note_13101233 It could be `status=any` or `sha=DEADBEAF`

## What are the relevant issue numbers?

Part of #4255

## 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)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [ ] 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)

See merge request !5347

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

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

Improve grammar of manual actions documentation

## What does this MR do?

Improve grammar of manual actions documentation

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

## Why was this MR needed?

Because people like good grammar.

## What are the relevant issue numbers?

## Screenshots (if relevant)


See merge request !5382

Add support for inline videos in issue, MR and notes (on issue, commit, MR, and MR diff)

## What does this MR do?

It adds support for inline videos in issue, MR and notes (on issue, commit, MR, and MR diff). Most of the work was done by @hayesr in !3508 but a few improvements were still missing.

## Why was this MR needed?

To be able to play uploaded videos in GitLab!

## What are the relevant issue numbers?

Closes #4142.

## Screenshots

### Video players

![Screen_Shot_2016-07-19_at_18.44.09](/uploads/e85e531b455a41c3e66b26b356abaafd/Screen_Shot_2016-07-19_at_18.44.09.png)

-----

![Screen_Shot_2016-07-19_at_18.44.29](/uploads/05f52a812760210d1eae86a7f8fc48bc/Screen_Shot_2016-07-19_at_18.44.29.png)

-----

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- Tests
  - [x] Test `VideoLinkFilter`
  - [x] Test in `spec/features/markdown_spec.rb`
  - [x] Improve `spec/uploaders/file_uploader_spec.rb`
  - [x] All builds are passing
- [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)

See merge request !5215

Use Re-deploy button on Deployments page

## What does this MR do?
Change `Retry` to `Re-deploy` which is more accurate.

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

## Why was this MR needed?

## What are the relevant issue numbers?
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/18885

## 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 [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)

See merge request !5374

`.ogg` is for music files.
Signed-off-by: Rémy Coutable <remy@rymai.me>