Update mail_room gem

## What does this MR do?

Upgrades the mail_room gem from 0.8.0 to 0.8.1.

## Why was this MR needed?

mail_room throws an exception if the watching script joins a undefined thread. Release 0.8.1 adds a check to ensure that the thread exists before calling join.

Fixes gitlab-org/omnibus-gitlab#1619.

See merge request !6714

Remove redundant images from GitLab basics docs



See merge request !6799

Add an example for testing a phoenix application with Gitlab CI

_Originally opened at !5074 by @nahtnam._

- - -

## What does this MR do?

Add an example on how to setup testing on phoenix 

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

Grammar and formatting

## Why was this MR needed?

https://twitter.com/gitlab/status/749898132008337408

## 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
  - [ ] All builds are passing
- [ ] 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 !6794

Replace images in GitLab basics docs



See merge request !6786

[ci skip]

Precalculate trending projects

## What does this MR do?

This MR changes the trending projects code so that data is precalculated, removing the need for any complex caching mechanisms. 

## Why was this MR needed?

Caching of trending data didn't work properly, still leading to queries. Using caching in general would be very hard due to users being able to apply custom filters to the list of trending projects.

See merge request !6749

Allows empty merge requests for a workflow described in gitlab-org/gitlab-ce#14606

Closes gitlab-org/gitlab-ce#14606

See merge request !6384

[ci skip]

Add `robots.txt` to the list of reserved namespaces

See #22759

See merge request !6789

Bump mail_room to v0.8.1 to fix thread cleanup issue

See https://github.com/tpitale/mail_room/blob/master/CHANGELOG.md

Closes #20273

See merge request !6788

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

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

Remove NamespacesController

* removes unnecessary NamespacesController. The main purpose of this controller was redirect to group or user page when URL like https://gitlab.com/gitlab-org was used. Now this functionality is handled by constrainers (like this https://gitlab.com/gitlab-org/gitlab-ce/blob/master/config/routes/user.rb#L17-21) and take user to correct controller right from the start.
* serve non existing API routes like `/api/v3/whatever` with Grape instead of Rails. Before this change wrong API url was served by rails with not obvious 404, 405 & 500 errors


See merge request !6733

Formatted all app/assets/javascripts to underscore naming convention

## What does this MR do?

Changes all javascript file names to user underscores as delimiter.

This will be enforced in the docs in a different MR !6782.

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

## Why was this MR needed?

Consistency.

## 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 it does - 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 #23118

See merge request !6783

Closes #20273

Changed 'Compare branches, tags or commit ranges' to 'Compare Git revisions'

## What does this MR do?

I remember we had a quick discussion about what to call the expected input of the compare page. Today whilst doing !6766 I found these are called [git revisions](https://git-scm.com/docs/gitrevisions).

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

## Why was this MR needed?

## Screenshots (if relevant)

![Screen_Shot_2016-10-10_at_14.44.13](/uploads/694200b8f56967d8e7caa965bbf7c123/Screen_Shot_2016-10-10_at_14.44.13.png)

Dunno where that gradient came 😆 Screenshot issue not code.

## 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 it does - 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 !6774

Changed network input placeholder to 'Git revision'

## What does this MR do?

Changes the commit SHA-1 input placeholder on the network page to `Git revision`. ([as defined here](https://git-scm.com/docs/gitrevisions))

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

## Why was this MR needed?

Placeholder was too complex

## Screenshots (if relevant)

![Screen_Shot_2016-10-10_at_15.06.23](/uploads/e31586b0f7a973b04e55e73223a2a95c/Screen_Shot_2016-10-10_at_15.06.23.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 it does - 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 #20356

See merge request !6766

Fix inconsistent options dropdown caret on mobile viewports

## What does this MR do?
Change the options dropdown caret from left aligned to right aligned (only visible on mobile viewports)

## Are there points in the code the reviewer needs to double check?
Check if there are any other dropdowns that have left aligned carets

## Why was this MR needed?
Resolve UI inconsistency as some dropdown carets were already right aligned

## Screenshots (if relevant)
Before:
![Simulator_Screen_Shot_Sep_15__2016__11.54.55_AM](/uploads/767d9344db4973af5a5368d5149144cc/Simulator_Screen_Shot_Sep_15__2016__11.54.55_AM.png)

After:
![Simulator_Screen_Shot_Sep_15__2016__11.54.09_AM](/uploads/882614cb9c5f85bf44e118cd7c74fcef/Simulator_Screen_Shot_Sep_15__2016__11.54.09_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 #22086

See merge request !6372

Added copy file path button to diffs

## What does this MR do?

Adds a copy file path button in the header of diff files.

## Screenshots (if relevant)

![Screen_Shot_2016-10-10_at_09.59.48](/uploads/1aedd5033bb3c1893023bb8c8d99a708/Screen_Shot_2016-10-10_at_09.59.48.png)

## What are the relevant issue numbers?

Closes #23108

See merge request !6769

Remove redundant mixins

## What does this MR do?
Removes the following redundant mixins
```
@mixin box-shadow($shadow) {
  box-shadow: $shadow;
}

@mixin border-radius($radius) {
  border-radius: $radius;
}
```

## Are there points in the code the reviewer needs to double check?
Just need to make sure the refactor didn't break anything. Last time I did something like this, we faced an edge case where values `.5` would pass correctly in mixins but not when passed directly to the property.

## Why was this MR needed?

*  Reduces redundant code which leads to happier developers 😄 

## Screenshots (if relevant)
None

## 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 #22012

See merge request !6287

[ci skip]

Add link to test coverage report to README

## What does this MR do?

Since we have GitLab Pages with test coverage report, it makes sense to link coverage badge there, instead of linking to commits page.

See merge request !6772

Rename HTMLEntityFilter to HtmlEntityFilter to fix autoloading

See merge request !6776

Use user from let instead recreate in before

## What does this MR do?
It`s minor fix in tests. We can use factory from let instead recreate user before each test.
 
## Are there points in the code the reviewer needs to double check?
No

## Why was this MR needed?

## Screenshots (if relevant)
No

## 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
  - [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 it does - 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 !6762

Improve backup doc readability

From https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3761

See merge request !6781

[ci skip]

Explain the extra chmod

There is confusion about what passing `0600` to File.open does.

```
$ touch /tmp/foobar
$ ls -l /tmp/foobar
-rw-r--r--  1 jacobvosmaer  wheel  0 Sep 26 14:20 /tmp/foobar
$ ruby -e 'File.open("/tmp/foobar", "w", 0600)'
$ ls -l /tmp/foobar
-rw-r--r--  1 jacobvosmaer  wheel  0 Sep 26 14:20 /tmp/foobar
$ 
$ 
$ rm /tmp/foobar
$ ruby -e 'File.open("/tmp/foobar", "w", 0600)'
$ ls -l /tmp/foobar
-rw-------  1 jacobvosmaer  wheel  0 Sep 26 14:21 /tmp/foobar
```

See merge request !6523

Changes to make Git basics more intuitive

From https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6420

See merge request !6777