Highlight note code and edit preview

More highlighting fixes! Highlighting wasn't applied all the way for
code in notes, diff notes diffs and diff preview (on the file edit page).

The CSS changes further unify the styling for file-content highlighting,
diff highlighting and note code highlighting.

See merge request !2594

Update rails, rails-html-sanitizer, and nokogiri for security fixes

See https://dev.gitlab.org/gitlab/gitlabhq/issues/2643

See merge request !2603

Rails updated to 4.2.5

I hope it'll fix weird spec failing (according to https://github.com/rails/rails/pull/22383)

@dzaporozhets @yorickpeterse 

See merge request !2591

Make deleted line background color for Solarized Dark a little darker

The difference is very slight, and I don't even _use_ Solarized Dark, but this annoyed me.

See merge request !2563

Diff highlight themes

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/12484

See merge request !2530

Allow empty Mysql password on CI

[ci skip]

See merge request !2558

Fix Error 500 when doing a search for merge requests

Potential fix for #11547

See merge request !2525

Remove unreleased note from changelog (8-4-stable)



See merge request !2556

[ci skip]

Fix grammar and typos in file finder docs



See merge request !2547

Fix MR diff 'Edit' button

It now works and has the right size.

See merge request !2542

More highlighted diff fixes

See merge request !2545

Make sure non-highlighted diffs are still escaped

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/12521

See merge request !2544

File finder can be invoked from anywhere!



See merge request !2543

Add method to calculate total size of artifacts in subpath

See merge request !2500

Add file finder documentation

Closes #7966 

See merge request !2541

Do not use progress bar when downloading build artifacts

Closes #12491

See merge request !2531

Added cache:key to .gitlab-ci.yml allowing to fine tune the caching

The `cache:key` allows you to define the affinity mask of caching, allowing to have single cache for all jobs, or cache per-job, or per-branch, or any other way you would need:

1. Cache per-build for all branches:

```
cache:
    key: "$CI_BUILD_NAME"
    untracked: true
```

2. Cache per-branch for all jobs:

```
cache:
    key: "$CI_BUILD_REF"
    untracked: true
```



/cc @DouweM @grzesiek @axil


See merge request !2436

Add housekeeping feature documentation

Add documentation about the new housekeeping feature in the project settings page.

See merge request !2371

Add basic documentation for build artifacts

/cc @axil @ayufan 

See merge request !2511

Add documentation on restarting GitLab

This will save as time from writing the same commands
over and over again.

See merge request !2510

Remove execution permissions from font assets

[ci skip]

See merge request !2082

Init script changes for gitlab-workhorse in 8.4

Goes with https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/31

Also bumps gitlab-workhorse to 0.6.1.

[ci skip]

See merge request !2529

Fix import of GitHub's wiki when the repository has not been created

Fixes #12503 

See merge request !2533

Creator should be added as a master of the project on creation

Fixes #4222 

This also enable a project creator to add themselves as a master of the
project for existing repositories that were created in the meanwhile
that they don't appear as members.

See merge request !2520

[ci skip]

Fix cross projects detection when importing GitHub pull requests

Fixes #12456

See merge request !2523

Added documentation for GitLab Metrics

This adds documentation for the metrics code I recently added.

Two notes:

* I'm referring to this feature as "GitLab Metrics" everywhere simply
  because the code resides in the `Gitlab::Metrics` namespace. A
  different name is fine, though I think just "Metrics" might be a bit
  too abstract.
* Grafana isn't covered since it's fairly straight-forward to setup
  (there's nothing really special we can cover). I think we _should_
  cover it once we start shipping it with Omnibus.

I assigned @axil since he's our technical writer/documentation guru,
feel free to re-assign if needed.

cc @sytses @axil @dzaporozhets @JobV 

See merge request !2484

Add syntax highlighting to diff view

Closes #3945

See merge request !2109

Split from !2455

References #9092

See merge request !2515

Gracefully handle invalid UTF-8 sequences in Markdown links

Closes #6077

See merge request !2382

Add sentry integration

Sentry is an event logging platform primarily focused on capturing and
aggregating exceptions. With this MR it will be possible to log and
track exceptions from GitLab to Sentry.

https://gitlab.com/gitlab-com/operations/issues/39

See merge request !2485

Fixes tooltip doesn't duplicate the "me" name.

Checks that "me" is not in the array of names in tooltip

![emojilist](/uploads/20b1a39cda194358f9730ec3c6b86acb/emojilist.gif)

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/7978


See merge request !2454

Adds "t" as a shortcut for find file anywhere



See merge request !2507

Remove `Compressed to` column from build artifacts browser

See #10982.

See merge request !2509

Use ENV variables for Unicorn worker killer & increase default limits

Merge request that lead to this particular merge request:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2421

[ci skip]

See merge request !2513

- Add attribution for Anton Baklanov
- Remove attributions for employees

[ci skip]