Add flexbox to project header

## What does this MR do?
Adds flexbox to project header to keep components vertically centered regardless of description presence/length

## What are the relevant issue numbers?
Closes  #18080 

## Screenshots (if relevant)
![Screen_Shot_2016-06-01_at_12.02.42_PM](/uploads/edd769110b52ec34046f4079619e45eb/Screen_Shot_2016-06-01_at_12.02.42_PM.png)     
![Screen_Shot_2016-06-01_at_12.02.35_PM](/uploads/c5c2828ba5688a2588d3721a2d21d5fe/Screen_Shot_2016-06-01_at_12.02.35_PM.png)

See merge request !4417

Change color of canceled ci text to gray

## What does this MR do?
Change text color of Canceled builds from `$gl-danger` to `$gl-gray`

## What are the relevant issue numbers?
Closes #18074 

## Screenshots (if relevant)
<img src="/uploads/f2ac59c5081c31cfb34bdc0470e31384/Screen_Shot_2016-06-01_at_10.38.17_AM.png" width="600px">

See merge request !4412

Bump recaptcha gem to 3.0.0 to remove deprecated stoken support

Google deprecated the use of stoken in its reCAPTCHA, so this gem is
necessary to make things work again.

Closes #18210 

See merge request !4484

Optimise email CSS for speed with Premailer

Speed up emails-on-push by removing all descendant selectors from the
CSS they use, which can make the CSS inlining much more efficient in
certain cases.

See: https://gitlab.com/gitlab-org/gitlab-ee/issues/490

See merge request !4511

Bump nokogiri to 1.6.8

Number of important security and bug fixes. See:
https://github.com/sparklemotion/nokogiri/blob/master/CHANGELOG.md#168--2016-06-06

See merge request !4500

Closes #18210

Load knapsack in Rakefile only when is bundled

Fixes `production` builds: https://dev.gitlab.org/gitlab/omnibus-gitlab/builds/85407

cc @marin 

See merge request !4514

Notifications dropdown on project page now has descriptions

## What does this MR do?

Adds descriptions to the notification settings dropdown on project pages. Also changed the order of them to make more sense.

## What are the relevant issue numbers?

Part of #12758

## Screenshots (if relevant)

![Screen_Shot_2016-05-31_at_09.35.24](/uploads/b30d82701a13ec15f672139e1225acf5/Screen_Shot_2016-05-31_at_09.35.24.png)

See merge request !4374

Add License Finder information to contribution acceptance criteria.

To make it clear what should be done when the license finder test fails.

cc: @stanhu 

See merge request !4512

Sub navigation

## What does this MR do?
Styles sub nav   
cc @dzaporozhets  @skyruler @jschatz1 

## What are the relevant issue numbers?
#18058 and #17983 

## Screenshots (if relevant)
![Screen_Shot_2016-06-03_at_12.10.26_PM](/uploads/8b948c32699a93ab0a390bda31e0e411/Screen_Shot_2016-06-03_at_12.10.26_PM.png)
![Screen_Shot_2016-06-03_at_12.10.34_PM](/uploads/241115c35d0618f3de739be9a670416d/Screen_Shot_2016-06-03_at_12.10.34_PM.png)

See merge request !4468

Implement compact side nav

## What does this MR do?
Implements new compact nav design   
Note- new navbar icons are in a separate MR (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4268)

## What are the relevant issue numbers?
Closes #18013 

## Screenshots (if relevant)
![Screen_Shot_2016-06-02_at_3.20.37_PM](/uploads/d31bd17ae47743f1a20d7429b4396e84/Screen_Shot_2016-06-02_at_3.20.37_PM.png)   
![Screen_Shot_2016-06-02_at_3.20.43_PM](/uploads/d03a080a57707b6a2161127f3904fcd5/Screen_Shot_2016-06-02_at_3.20.43_PM.png)

cc @dzaporozhets 

See merge request !4447

Instrument `RepositoryCheck::SingleRepositoryWorker` manually

See merge request !4446

This worker is called manually by `RepositoryCheck::BatchWorker` meaning it's not tracked automatically by the Sidekiq middleware.

Add new GitLab CI configuration facade class

## What does this MR do?

This MR is a first iteration of major CI configuration refactoring. See #17139 and #15060 for more details.

## What are the relevant issue numbers?

Closes #17139

See merge request !4462

Number of important security and bug fixes. See:
https://github.com/sparklemotion/nokogiri/blob/master/CHANGELOG.md#168--2016-06-06

Ability to prioritize labels

Closes #14189 

See merge request !4009

Fix knapsack for master

It were mistakenly to invoke `rspec` where it should invoke `spinach`.


See merge request !4510

This is part of #12758

Use Knapsack to evenly distribute specs

Try to distribute all tests evenly accross all nodes to reduce the testing time of GitLab CE.

This uses high amount of auto-scaled machines.


See merge request !4240

Added 8.9 install/update guides

See merge request !4507

[ci skip]