Add letter_opener_web gem

Sent emails in the development environment will no longer automatically
be opened in the browser. If a sent email needs to be viewed, it can be
found at the `/rails/letter_opener` route.

See merge request !3893

Add button to toggle whitespace changes

Closes #4271 

**Merge Request**

<img src="/uploads/ea857269faed38a25b63b768d7f3a85b/Screen_Shot_2016-03-23_at_11.32.41_AM.png" width="1157" />


**Diff view**

<img src="/uploads/bc2ac3e4855584f9214c8f3ddf325b06/Screen_Shot_2016-03-23_at_11.32.53_AM.png" width="1211" />

See merge request !3367

Reduce width of parallel diffs

At 50% width the alignment is off on parallel diffs (see https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3785/diffs and view in Side-by-Side)  
Reducing width lines them up:

<img src="/uploads/5775d35b0e86397abd10db6195a8a54d/Screen_Shot_2016-04-22_at_2.19.21_PM.png" width="400px">

Also shifted comment button over to center it properly:  
<img src="/uploads/c2468e15bb65523464a941001c3d7298/Screen_Shot_2016-04-22_at_2.24.33_PM.png" width="200px">

See merge request !3891

Increase screen width breakpoint for hide/show discussion

Closes #15606

See merge request !3915

Allow alternative names for the CHANGELOG file.

"CHANGELOG", "NEWS", "HISTORY", and "CHANGES" are recognized as Changelog files.

Also adds relevant tests for each of these names.

Resolves #14864.

See merge request !3768

"CHANGELOG", "NEWS", "HISTORY", and "CHANGES" are recognized as Changelog files.

Also adds relevant tests for each of these names.

Resolves #14864.

Remove devise async

The extra gem isn’t necessary anymore since Devise + Rails 4.2 has ActiveJob integration.

Fixes #15575. Working towards #14286.

cc: @dzaporozhets @rspeicher 

See merge request !3902

Add usage example for the Office 365 GetPersonaPhoto-service.



See merge request !2462

The extra gem isn’t necessary anymore since Rails 4.2 has ActiveJob integration.

Resolves #15575.

Do not fsck projects less than a day old

This should bring the number of false positives down.

Helps https://gitlab.com/gitlab-org/gitlab-ce/issues/15423

See merge request !3926

Fixed width of .search-location-badge as it was causing issues in Safari.

Fixed width of .search-location-badge as it was causing issues in Safari.

Fixes issue #15541 and is a minor CSS only change so [ci skip]

# Before

Safari:
![Screen_Shot_2016-04-24_at_22.35.38](/uploads/74388670fde3af94429d83b954833bd3/Screen_Shot_2016-04-24_at_22.35.38.png)

# After

Safari:
![Screen_Shot_2016-04-24_at_21.59.49](/uploads/177d0d8fda665165dff5006930604fc6/Screen_Shot_2016-04-24_at_21.59.49.png)

Chrome:
![Screen_Shot_2016-04-24_at_21.59.40](/uploads/6764cd5864901210f4f8eff4388fd6db/Screen_Shot_2016-04-24_at_21.59.40.png)

# CSS class referenced in the following files:

`./app/assets/javascripts/search_autocomplete.js.coffee`

`./app/assets/stylesheets/pages/search.scss`

…and is visible on the search bar on every page.

See merge request !3900

Emphasize that GitLab must be partially running when restoring backups.

This caused me a lot of pain until I caught on.
I also enhanced the GitLab Omnibus application data backup restore procedure.  I verified the procedure by executing it with GitLab 8.6.4.

See merge request !3844

Search ui update

Closes #2537 

See merge request !3751

This reverts merge request !3839

Document that only unicorn and sidekiq should be stopped.

And the rest of GitLab should remain running.
Also clarified the rest of the GitLab Omnibus restore procedure.

See merge request !3839

Update PROCESS.md

Fix grammar by adding missing "we" 
Add extra newline so example isn't part of list.

See merge request !3845

This should bring the number of false positives down.

Throttle the update of `project.last_activity_at` to 1 minute

This implement [the solution](https://gitlab.com/gitlab-org/gitlab-ce/issues/15094#note_4769387) proposed by @jacobvosmaer.

See merge request !3848

Changed some variable names
Fixed CHANGELOG entry

Correct search results count

CHANGELOG item