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

Implement new UI for pagination

Fixes #6063 ![Screenshot_2016-01-20_09.38.59](/uploads/f50d333bdb6cb9683848fb0a874241ef/Screenshot_2016-01-20_09.38.59.png)


See merge request !2517

Fix term height so text overflap does not happen.

Fixes #12449 

Height was set on the `.term`. It made the text overlap. 

See merge request !2518

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]

[ci skip]

Adds disabled comment field and disabled avatar.

Fixes #3540

![Screen_Shot_2016-01-20_at_12.13.29_AM](/uploads/673fb783e9aeae441df9c40bfe29ac1b/Screen_Shot_2016-01-20_at_12.13.29_AM.png)


See merge request !2508

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

Fix cross projects detection when importing GitHub pull requests

Fixes #12456

See merge request !2523

[ci skip]

This also enable a project creator to add themselves as a master of the
project.

[ci skip]

Add syntax highlighting to diff view

Closes #3945 

See merge request !2109

Mention required Ruby version

Closes #12446

See merge request !2524

[ci skip]

Add note about minimum GitLab CI version

Documentation update: To use variables in `.gitlab-ci.yml` it's not enough to update the GitLab Runner, a minimum version of GitLab CI is needed as well.

See merge request !2514

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

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

Upgraded gitlab_git to fix issue #5858

This updates the dependency on gitlab_git and fixes #5858 - reproduced locally and issue disappears with the change.

Related MR that actually adds branch name support to commits_between: https://gitlab.com/gitlab-org/gitlab_git/merge_requests/61

See merge request !2516

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

Fixed invalid JSON in first JSON Example

Just a comma missing

See merge request !2487