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]

Added X-GitLab-... headers to emails from CI and Email On Push services

Fixes #2098

This adds the 'X-GitLab-Project', 'X-GitLab-Project-Id' and
'X-GitLab-Project-Path' headers to emails from CI and Email On Push in a way
that it is done currently for merge requests and issues emails.

Additionally, CI emails will have 'X-GitLab-Build-Status' header with either
'fail' or 'success'.

Emails from Email On Push will include 'X-Gitlab-Author' header containing the
username of user who did the push.

See merge request !2159

Starring project only increases star count

This is instead of increasing star & fork count

Fixes #11396

![star-count](/uploads/9a1d569393bc051d1a019f0340eec957/star-count.gif)

cc. @jschatz1 

See merge request !2504

Allow LDAP users to change their email if it was not set by the LDAP
server

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/3054

See merge request !2502

Fix double request issue in artifacts browser

This fixed problem with double propagation when clicking a link that lies inside tr with clicked event attached.

See merge request !2496

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

Fixes: #4222

See merge request !2463

Greatly improve external_issue_tracker performance

See 3d41133d48f6522b8755bb91b804864e8e520871 for all the details. As an aside, this commit contains a set of migrations that will introduce downtime as they add a column with a default value which in turn locks the entire table (at least on PostgreSQL).

See merge request !2498

Fix positioning issues with browse files button

Issue is that in Firefox clipboard is blocking the browse files
from moving all the way to the right.
Move clipboard up 1px into -1px to unblock "browse files"

SS from firefox:

![Screen_Shot_2016-01-18_at_4.01.58_PM](/uploads/312a5f1e55ca707081f718e2413416fb/Screen_Shot_2016-01-18_at_4.01.58_PM.png)

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/10849


See merge request !2489

Reduce margin to fit dropdowns

![Screen_Shot_2016-01-18_at_7.51.23_PM](/uploads/03336f86fde25d6d045742297a19751c/Screen_Shot_2016-01-18_at_7.51.23_PM.png)

Fixes #10747 

See merge request !2492

Improve UX in build artifacts browser

This improves UX in build artifacts browser, and makes it more consistent with repository tree browser we already have.

---
Before:

![ux_artifacts_before](/uploads/9869ff74afd5e6636f0df81c7823fb6f/ux_artifacts_before.png)

---
After:

![ux_artifacts_after](/uploads/cdb68925f4489bb852fd701870e6d6a0/ux_artifacts_after.png)

---

It is easier to click on a file/directory entry now, because we don't need to click on a entry's basename (that can be really short, like `..` parent directory). We also show `Compressed to` size that indicates how much storage does this entry really consume.

Row for an entry is also highlighted on hover and we do not have Download button (clicking on a file row / file basename is enough to download a file).

Closes #10242 

See merge request !2477

Move entry `Fix: As an admin, cannot add oneself as a member to a
group/project`

The CHANGELOG entry said it was fixed in 8.2.3. However, I found
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/1942 that
suggests it wasn't fixed until 8.3.0. A customer experienced this
issue on 8.2.3, still. This ultimately led to me investigating this
further.

[ci skip]

See merge request !2488

Fix limit for `data` column in `events` table when using MySQL

Closes #9084 

See merge request !2486

Update devise to version 3.5.4

Closes https://dev.gitlab.org/gitlab/gitlabhq/issues/2642

See merge request !2490

Remove leading comma when user is the only one to award that emoji

Fixes #9073

See merge request !2450

Use gitlab-workhorse 0.6.0

[ci skip]

See merge request !2483

Ensure Gravatar host looks like an actual host

Solves #10243.

I've chosen to simplify the method that extracts the host: since we
only need the host, let's get rid of the path and thus get rid of the
escaping problems!

Unit tests should ensure that most of the cases are covered.

See merge request !2482

Fixes issue where firefox does not delete message after comment submit

Issue was **not** in the way comment was being submitted.
`app/assets/javascripts/awards_handler.coffee` was throwing an error.
This error was preventing any js from running after it.
Fixes #1473

See merge request !2452

Issue page keeps jumping up

This happens when the discussion side is smaller than the sidebar and the sidebar will need to scroll. When this happens I calculate the height of the two and see if the discussion panel is smaller and make them the same height and add a class `no-affix` which makes the sidebar relative positioning so it won't stick to the top.

See merge request !2417