Improve emoji picker

This request uses an emoji image sprite to show big set of emojis. The sprite has been made based one gemojione gem images. The categories are retrieved from https://github.com/jonathanwiesel/gemojione/blob/master/config/index.json as well.

Some categories are pretty poor, it can be extended in the future.

It's a first step on the way to improve picker.

The first implementation was using https://github.com/iamcal/emoji-data project, but there was huge incompatibility with gemojione emojis set and I had to drop that solution.

![Screenshot_2015-12-22_23.26.27](/uploads/7d323eb0586204ac92915b41233b97ec/Screenshot_2015-12-22_23.26.27.png)


See merge request !2172

Make CI Lint form synchronous

This removes `remote: true` from CI Lint form, making it synchronous
form. This also removes some complexity related to displaying lint
messages.

View also has been updated, removed deprecated Bootstrap 2 tags.
Improved design.

See merge request !2171

Fix and test leave project display

The 'Leave this project' display on project page was broken. It was calling the method incorrectly, which returned `nil` and displayed nothing. 

This fixes the display and also adds 2 different tests for it.

cc/ @jvanbaarsen @stanhu Please review and merge if you think it looks good. Thank you!

See merge request !2166

New group page

Implementing from https://gitlab.com/gitlab-org/gitlab-ce/issues/3480#note_2722988

cc @skyruler 

For https://gitlab.com/gitlab-org/gitlab-ce/issues/3480

See merge request !2174

Hotfix for sidekiq-cron being loaded from Settingslogic with defaults

This fixes a regression with "Stack level too deep" from master.

See merge request !2173

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

New colour scheme

old
![Screenshot_2015-12-17_14.14.53](/uploads/5d6ac28b6d99186485d727a72cc8a662/Screenshot_2015-12-17_14.14.53.png)

new
![Screenshot_2015-12-17_14.15.07](/uploads/06e07fa3716aa8664b1507b390270285/Screenshot_2015-12-17_14.15.07.png)

* Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/2577

See merge request !2151

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Sidekiq-cron configuration moved to gitlab.yml

When `sidekiq-cron` was introduced, jobs configuration where placed
in `schedule.yml` file.

As discussed in #3928, this is not desirable. 
We moved it to `gitlab.yml`, exposing only the "cron" part of the configuration.

See merge request !2087

This removes `remote: true` from CI Lint form, making it synchronous
form. This also removes some complexity related to displaying lint
messages.

View also has been updated, removed deprecated Bootstrap 2 tags.
Improved design.

Closes #4206

Fix MR 500 when viewing the MR page

Fixes #2712 

See merge request !2167

Explicitly require Nokogiri 1.6.7.1 due to security issue

```
Name: nokogiri
Version: 1.6.7
Advisory: CVE-2015-5312
Criticality: High
URL: https://groups.google.com/forum/#!topic/ruby-security-ann/aSbgDiwb24s
Title: Nokogiri gem contains several vulnerabilities in libxml2
Solution: upgrade to >= 1.6.7.1
```

See merge request !2154

Also, make it not fail.

This is required since we parse URI later and remove the credentials

Also adds a spec for MergeRequestHelper to avoid having a regression
later on.

[ci skip]

Fixed wrong URL to "up for grabs" issue filter

[ci skip]

See merge request !2162

Allow admin to create new user identities

Fixes #2442 

See merge request !2077

Fix issue related cross-project MRs

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/4188

See merge request !2163

Allow account unlock via email

We see a lot of users get confused about what it means when your account gets
locked. Many try to reset their password and are still faced with a lockout.
With this change, users receive an email that allows them to unlock their
account immediately. The previous behavior where the account is auto-unlocked
after a time also still works.

See merge request !2049