Use ActionDispatch Remote IP for Akismet checking

Previously all remote IPs appeared at 127.0.0.1, which made Akismet
not very useful. Using the ActionDispatch Remote IP (http://api.rubyonrails.org/classes/ActionDispatch/RemoteIp.html)
should provide more reliable results.

Closes #16629

See merge request !3961

Users can use the feature proposal label inside the issue

Got the idea from https://gitlab.com/gitlab-org/gitlab-ce/issues/12620.

\cc @JobV @sytses 

See merge request !2574

Send 'admin emails' weekly, not daily

Daily seems to be to spammy, so let's default to weekly instead.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15520

See merge request !3923

[ci skip]

Update using_docker_build.md, clarify the 'privileged' mode requirement

Related to #15428

Fixes gitlab-org/gitlab-ci-multi-runner#1261

See merge request !3909

[ci skip]

Backport GitHub Enterprise import support from EE

These changes were pulled from GitLab EE to support configuring
an alternative API URL than the default https://api.github.com.
In addition, the `verify_ssl` flag allows users to disable SSL cert
checking.

One modification: add a default `args` option if it does not exist
to avoid breaking existing configurations.

See merge request !3892

Previously all remote IPs appeared at 127.0.0.1, which made Akismet
not very useful. Using the ActionDispatch Remote IP (http://api.rubyonrails.org/classes/ActionDispatch/RemoteIp.html)
should provide more reliable results.

Closes #16629

Add JS prefix to user tab classes

## What does this MR do

This MR adds the `js-` prefix to the classes which are used for js purposes only. This MR only affects the said classes inside `users/show.html.haml`.

## Are there points in the code the reviewer needs to double check?

I'm not entirely sure if this project uses the `js-` prefix for
classes that are used for js purposes only. Doing a grep shows some of the classes have the prefix, but I'm still unsure whether this project follows this rule.

## Why was this MR needed?

As I was working thru #13401, I wanted to add a tab on the user profile page to show the contributions outside the GitLab instance. Reading the JS, I came across this. This MR helps new people reading the code that the said classes are for js purposes only. Also, it helps the project work toward to uniform class naming.

I suggest that we document adding the `js-` prefix to classes for js purposes only (if this is the case for this project)

See merge request !3928

Add API doc example with query string for triggering build

Make this explicit to prevent confusion as we saw in gitlab-org/gitlab-ci#413.

See merge request !3947

Sidekiq MemoryKiller sends a `SIGKILL` signal, not `SIGTERM`

As documented in https://gitlab.com/gitlab-org/gitlab-ce/blob/f127edd012bd8b6f76ac67d69aadbd7d4837258f/lib/gitlab/sidekiq_middleware/memory_killer.rb#L10 (this was changed by c291ff9c).

See merge request !3927

Project title dropdown tests

Added a test for when on an issue page to check whether the project
dropdown links will still work

See !3870

See merge request !3921

Updated label links to work correctly for filtering

See !3846#note_5033951

See merge request !3920

Escape key closes the dropdown

Fixes #15432 

![esc](/uploads/067e32bcaf265c3241d84dcbd3f11532/esc.gif)

See merge request !3904

Changes support from IE 10+ to IE 11+

IE 11 was released 17 October 2013; 2 years ago. Generally what I have experienced is that support for browsers (when newer ones are available) continues for up to 2 years. Based on that info we would drop support for IE 10 and the latest IE we would support would be IE 11. 

I also think this is more realistic since no one is really testing anything on IE 10 at the moment.  We should start testing on all the browser that we currently support. 

Also we can then have real support for flexbox and not need things like `-ms-flexbox` and other IE specific hacks. 

cc @iamphill @annabeldunstone @elvongray @alfredo1 @rspeicher 

See merge request !3913

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

These changes were pulled from GitLab EE to support configuring
an alternative API URL than the default https://api.github.com.
In addition, the `verify_ssl` flag allows users to disable SSL cert
checking.

One modification: add a default `args` option if it does not exist
to avoid breaking existing configurations.

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