Convert image diff background image to CSS

## What does this MR do?
Replaces the `trans_bg.gif` image used for image diff background image with a CSS implementation of the same background image

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

## Why was this MR needed?
Uses CSS to replace the use of an image so that webpage rendering is slightly improved

## What are the relevant issue numbers?
Closes #20500 

## Screenshots (if relevant)
Before:
![Screen_Shot_2016-08-01_at_12.29.10_PM](/uploads/8269877c561c29e6b0ca988079ff3fc6/Screen_Shot_2016-08-01_at_12.29.10_PM.png)

After:
![Screen_Shot_2016-08-01_at_12.29.16_PM](/uploads/cc88848b9c0e044445d19b889fd79271/Screen_Shot_2016-08-01_at_12.29.16_PM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [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 !5598

Add simple identifier to public SSH keys

## What does this MR do?
Adds a simple identifier of user_name + hostname to public SSH keys

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

## Why was this MR needed?
To help people identify keys when they export them

## What are the relevant issue numbers?
#18866 

## Screenshots (if relevant)

## 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
  - [ 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)
Closes #18866

See merge request !5614

Redirect to external issue tracker from `/issues`

Prior, in order to display the correct link to "Issues" in the project
navigation, we were performing a check against the project to see if it
used an external issue tracker, and if so, we used that URL. This was
inefficient.

Now, we simply _always_ link to `namespace_project_issues_path`, and
then in the controller we redirect to the external tracker if it's
present.

This also removes the need for the `url_for_issue` helper. Bonus! 🎉

See merge request !5608

Convert switch icon into icon font

## What does this MR do?
Converts the switch icon into the exchange icon from font awesome

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

## Why was this MR needed?

*  Decreases an external resource for the repository compare page
*  Icon font provides a sharper image for displays with higher pixel resolutions

## What are the relevant issue numbers?
Closes #20508 

## Screenshots (if relevant)
Before:
![Screen_Shot_2016-08-01_at_3.06.06_PM](/uploads/6ad46cc6dff98ec534e1f5a0fe556fa7/Screen_Shot_2016-08-01_at_3.06.06_PM.png)

After:
![Screen_Shot_2016-08-01_at_3.06.10_PM](/uploads/3cb11c40cbba398f9986a4cc6b3a7e4c/Screen_Shot_2016-08-01_at_3.06.10_PM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [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 !5603

link the engineering workflow document from process and contributing

## What does this MR do?

Add links to process and contributing to the engineering workflow document. 

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

no.

## Why was this MR needed?

The engineering workflow document is very important to Inc developers, but was hard to find.

## What are the relevant issue numbers?

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

not relevant

See merge request !5625

Allow branch names ending with .json for graph and network page

## What does this MR do?

Allow branch names to end with `.json` for graph and network page.

## Why was this MR needed?

Displaying branches ending on `.json` in repository view crashes because links to graph and network page can not be determined.

## What are the relevant issue numbers?

fixes #20462, #19585

See merge request !5579

Expand commit message width in repo view

## What does this MR do?
Expands the commit message width in repo view to take advantage of the unused white space (under the history href)

## Are there points in the code the reviewer needs to double check?
Just need to make sure there aren't any side effects

## Why was this MR needed?
To take advantage of the unused space on repo views

## What are the relevant issue numbers?
Closes #20225 

## Screenshots
Before:
![Screen_Shot_2016-07-27_at_11.10.22_AM](/uploads/1f2c604ac6d4ede2bac67179cfe77b20/Screen_Shot_2016-07-27_at_11.10.22_AM.png)

After:
![Screen_Shot_2016-07-27_at_11.08.55_AM](/uploads/34a36c884a06fd6cfd9b6512d1230196/Screen_Shot_2016-07-27_at_11.08.55_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] Added tests
  - [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 !5494

Add and update vendored templates for 8.11

[ci skip]

See merge request !5626

Fixed artifacts expire date in FF

## What does this MR do?

FireFox was trying to parse the date incorrectly so it would just show 'Past due'

## Screenshots (if relevant)

![Screen_Shot_2016-07-21_at_17.16.57](/uploads/938d39c648dc98540cd991cf552276dd/Screen_Shot_2016-07-21_at_17.16.57.png)

See merge request !5403

Speedup DiffNote#active? on discussions

See merge request !5597

Add es6 to teaspoon

## What does this MR do?

Adds the `es6` file extensions to teaspoon matchers so it can load those specs.

This also removes the current coffee matchers.

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

## Why was this MR needed?

We need to accept `.js.es6` specs.

## What are the relevant issue numbers?

## 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 !5524

Resolve ""CI configuration" button when `.gitlab-ci.yml` is present"

## What does this MR do?
Adds `CI configuration` button to project overview page

## What are the relevant issue numbers?
Closes #20101

## Screenshots (if relevant)
![Screen_Shot_2016-07-28_at_11.51.32_AM](/uploads/499d942d203d287ae98b7589ef12673c/Screen_Shot_2016-07-28_at_11.51.32_AM.png)



See merge request !5558

Remove outdated notes from the update guide

## What does this MR do?

updates guides

See merge request !5624

Speedup DiffNote#active? on discussions, preloading noteables and avoid touching git repository to return diff_refs when possible

- Preloading noteable we share the same noteable instance when more than one 
discussion refers to the same noteable.
- Any other call to that object that is cached in that object will be for any 
discussion.
- In those cases where merge_request_diff has all the sha stored to build a diff_refs get that 
diff_refs using directly those sha instead accessing to the git repository to first get the 
commits and later the sha.

fix runner install link

## What does this MR do?

Fix link to GitLab CI Runner installation

## Why was this MR needed?

Link is broken

See merge request !5612

Revert "md5 and utf_encode js libraries"

## What does this MR do?

Remove two unused JavaScript libraries (`md5.js` and `utf8_encode.js`).

## Why was this MR needed?

Those libraries were not used anymore:

```
$ find app/ lib/ -name '*.js' -exec grep --perl-regexp --with-filename '(md5|utf8_encode)' {} \;
app/assets/javascripts/lib/utils/utf8_encode.js:function utf8_encode (argString) {
app/assets/javascripts/lib/utils/utf8_encode.js:  // *     example 1: utf8_encode('Kevin van Zonneveld');
app/assets/javascripts/lib/utils/md5.js:function md5 (str) {
app/assets/javascripts/lib/utils/md5.js:  // -    depends on: utf8_encode
app/assets/javascripts/lib/utils/md5.js:  // *     example 1: md5('Kevin van Zonneveld');
app/assets/javascripts/lib/utils/md5.js:  str = this.utf8_encode(str);
```


See merge request !5613

Instrument the Repository class

## What does this MR do?

This MR instruments the Repository class.

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

No.

## Why was this MR needed?

This class wasn't instrumented.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [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 !5621

Since this isn't an ActiveRecord::Base descendant it wasn't
instrumented.

Add help document describing intended wiki linking behavior

Related to #16568
Closes #18019

- This documents the _intended_ behaviour of linking to wiki pages/files.

## TODO

- [x] Respond to @rymai's comments
    - [x] Use `succeed`
    - [x] Shouldn't this be <wiki_root>/miscellaneous.md here?
    - [x] what happens for file links that starts with a `/`?

See merge request !4372

Always compare with FETCH_HEAD in downtime_check

See merge request !5619

fix TODO comment

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/20376

After some testing, I've found out this wasn't needed and attachments seemed to work fine for import/export between instances (omnibus & source).

See merge request !5617

Only use RequestStore in ProjectTeam#max_member_access_for_users if it is active

See merge request !5604

This ensures this CI step works properly even when doing a shallow
clone.

Add support for relative links starting with ./ or / to RelativeLinkFilter

## What does this MR do?

- Allow explicit relative links in Markdown (starting with `./`).
- Allow absolute links (relative to the branch's root directory) in Markdown (starting with `/`).

## Why was this MR needed?

Those link types were not supported before.

## What are the relevant issue numbers?

fixes #19028

See merge request !5586

This reverts commit 1bba46d6.