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

Install unzip in build environment [ci skip]



See merge request !2593

Update gitlab_git & use new method for counting branches

Corresponding gitlab_git merge request detailing some of the rationale behind this: https://gitlab.com/gitlab-org/gitlab_git/merge_requests/62

Fixes #12418 

See merge request !2535

Admin area: doesn't show a note when it's empty

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/12636

See merge request !133

Add note on artifacts browser functionality

Based on the following comment:
https://gitlab.com/gitlab-org/gitlab-ce/issues/12634#note_3359006

See merge request !2586

Based on the following comment:
https://gitlab.com/gitlab-org/gitlab-ce/issues/12634#note_3359006

[ci skip]

Move supported omniauth providers to the top



See merge request !2585

[ci skip]

Move all integration docs images in a single directory



See merge request !2584

[ci skip]

Refactor system_hooks API documentation



See merge request !2475

Refactor namespaces API documentation



See merge request !2472

Refactor README API documentation

~~Waiting for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2435 to be merged.~~

See merge request !2476

[ci skip]

Refactor settings API documentation



See merge request !2474

[ci skip]

Refactor labels API documentation



See merge request !2471

Refactor issues API documentation



See merge request !2466

Refactor deploy_keys API documentation



See merge request !2467

Refactor branches API documentation



See merge request !2464

Don't vendor minified JS

Fixes #4031

See merge request !2494

Whitelist raw "abbr" elements when parsing Markdown

See #12517.

See merge request !2559

Forcefully install apt packages



See merge request !2577

Closes #12517

Ignore binary files in code search to prevent Error 500

Leaving out the -I option in "git grep" would cause an Error 500 because the
resulting line would include "Binary file X matches", which would cause the project search results to crash with the following error:

```
ActionView::Template::Error (wrong argument type nil (expected Regexp)):
    1: - blob = @project.repository.parse_search_result(blob)
    2: .blob-result
    3:   .file-holder
    4:     .file-title
  app/models/repository.rb:742:in `sub'
  app/models/repository.rb:742:in `block in parse_search_result_from_grep'
  app/models/repository.rb:741:in `each_line'
  app/models/repository.rb:741:in `parse_search_result_from_grep'
  app/models/repository.rb:682:in `parse_search_result'
  app/views/search/results/_blob.html.haml:1:in `_app_views_search_results__blob_html_haml__1959871337755590783_162450160'
  app/views/search/_results.html.haml:20:in `_app_views_search__results_html_haml__2198486911700532411_58329920'
  app/views/search/show.html.haml:7:in `_app_views_search_show_html_haml___1698304427272645201_62235300'
```

See merge request !2565

Make git gc man page more apparent



See merge request !2557

Remove gray background from issue/mr/milestone background

Fixes #6062 
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
cc @skyruler @creamzy 

See merge request !2573

Fix UI for pages with panels
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

cc @skyruler @creamzy 

Fixes #12633 

See merge request !2571