Display referenced merge request statuses in the issue description

See gitlab-org/gitlab-ce#3180 for original issue.
Previously discussed in !1941 and in !1771 before that.

* [x] Show a "Related Merge Requests" list on the issue page under the Description as given by the UI mockup
* [x] Display `all_references.merge_requests` and `note.all_references.merge_requests` 
* [x] Consider displaying the merge request status in addition to the CI status to enable complete merge request status understanding.

See merge request !1991

Revert removal of RedCloth

Revert !2037.

See merge request !2071

Fix delete notes on merge request diff

Fixes #3971

See merge request !2061

This reverts commit e426c027, reversing
changes made to c3676aa1.

Aling project js with EE

The MR ports the changes introduced by gitlab-org/gitlab-ee!70 in `project.js.coffee`.  


See merge request !2054

Enable rubocop metrics

This enables rubocop metrics like CyclomaticComplexity and ABCSize.
Initial threshold values are high, should be probably decreased.

See merge request !1802

Fix award-emojis alert flash message

This adds a new feature to `Flash` that allows to pin it after a
specified selector. This removes a fixed position from such award-emoji
alert, and makes it responsive by design of selector that this alert is
pinned to.

Closes #3996

\cc @vsizov 

See merge request !2065

This adds a new feature to `Flash` that allows to pin it after a
specified selector. This removes a fixed position from such award-emoji
alert, and makes it responsive by design of selector that this alert is
pinned to.

Closes #3996

Emoji aliases problem

Fixes #3850

See merge request !2064

Bump gitlab_emoji to ~> 0.2.0

A new version of this gem was released October 29th
but was never bumped in GitLab.

See merge request !1994

Expand character set of usernames created by Omniauth

When a user is created by Omniauth, Gitlab tries to assign the username based on the information provided in the auth hash. If no nickname is present, it uses the part of the email address before the @. This portion of the email address is run through the `parameterize` method, presumably to convert Unicode characters to ASCII.

`parameterize` strips out a number of characters that are valid in usernames. For example, `john.doe` is a valid Gitlab username, but parameterize will turn this into `john-doe`.

Instead of `parameterize`, this merge request uses `normalize` to convert non-ascii characters. This allows all acceptable characters to be used when creating a username from an email address. 

See merge request !660

Remove check icon from merged MRs

Now that GitLab CI exposes the status of each MR in the MR page it seems "redundant" to have an extra icon next to the CI statuses.

The "downside" is with people that don't use CI and don't see the statuses, but I don't think that this is that big a change that would miss to anyone.

\cc @dzaporozhets @creamzy 

How it looks now:

![screenshot-gitlab_com_2015-12-10_20-49-53](/uploads/414dcb5131eab2d9518dc77019116c96/screenshot-gitlab_com_2015-12-10_20-49-53.png)


See merge request !2059

Bump devise to 3.5.3 to fix reset token expiring after account creation

Also fixes an incorrect redirect after login with relative URL root:

Closes https://github.com/gitlabhq/gitlabhq/issues/8228

Closes #2750

See merge request !2056

Fix typos in all docs

Document file upload random uuid security

This documents the current state of file uploads regarding random UUID and security.
Fixes #3569 

Thanks to @DouweM for the language.

cc/ @sytses @JobV @axil Does this look OK?

See merge request !2055

Upgrade Sidekiq to 4.x

Upgraded Sidekiq to 4.x.
More details can be found here: #3065 

After merging this MR, we will require Redis 2.8+.

@stanhu have made a MR !1888 to reflect needed changes on our documentation.

See merge request !2057

Also fixes an incorrect redirect after login with relative URL root:

Closes https://github.com/gitlabhq/gitlabhq/issues/8228

Closes #2750

Fix editing notes on a merge request diff

Fixes #3910

See merge request !2041

Now that GitLab CI exposes the status of each MR
in the MR page it seems "redundant" to have an
extra icon next to the CI statuses.

Add missing changelog items

Closes #3973

[ci skip]

See merge request !2053

Reason: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2023