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

[Second try] Implement different Markdown rendering pipelines and cache Markdown

!1602 already got merged in bcd89a58, but it would appear the merge commit disappeared because of #3816 (or some other reason).

cc @rspeicher 

See merge request !2051

# Conflicts:
#	spec/lib/gitlab/markdown/autolink_filter_spec.rb
#	spec/lib/gitlab/markdown/commit_range_reference_filter_spec.rb
#	spec/lib/gitlab/markdown/commit_reference_filter_spec.rb
#	spec/lib/gitlab/markdown/cross_project_reference_spec.rb
#	spec/lib/gitlab/markdown/emoji_filter_spec.rb
#	spec/lib/gitlab/markdown/external_issue_reference_filter_spec.rb
#	spec/lib/gitlab/markdown/external_link_filter_spec.rb
#	spec/lib/gitlab/markdown/issue_reference_filter_spec.rb
#	spec/lib/gitlab/markdown/label_reference_filter_spec.rb
#	spec/lib/gitlab/markdown/merge_request_reference_filter_spec.rb
#	spec/lib/gitlab/markdown/redactor_filter_spec.rb
#	spec/lib/gitlab/markdown/reference_gatherer_filter_spec.rb
#	spec/lib/gitlab/markdown/relative_link_filter_spec.rb
#	spec/lib/gitlab/markdown/sanitization_filter_spec.rb
#	spec/lib/gitlab/markdown/snippet_reference_filter_spec.rb
#	spec/lib/gitlab/markdown/syntax_highlight_filter_spec.rb
#	spec/lib/gitlab/markdown/table_of_contents_filter_spec.rb
#	spec/lib/gitlab/markdown/task_list_filter_spec.rb
#	spec/lib/gitlab/markdown/upload_link_filter_spec.rb
#	spec/lib/gitlab/markdown/user_reference_filter_spec.rb

Run db:reset before db:create on CI

Should prevent build failures caused by missing migrations, such as
https://gitlab.com/gitlab-org/gitlab-ce/builds/439927

See merge request !2045

Enable Devise paranoid mode and ensure the returned message is the same
every time. This will prevent user enumeration (low impact). 

Prior to this change a user could type an email in the password reset
field and if the email didn't exist it returned an error. If the email
was valid it returned a message saying the forgot password link had been
emailed. After this change the user will receive a message that if the
email is in our database the reset link will be emailed. 

I also changed the throttle mechanism so it still works the same but
now returns the exact same message as above. Previously it would say
'You've already sent a request. Wait a few minutes'. This also allows
user enumeration, although it requires a double-check.

Related to https://dev.gitlab.org/gitlab/gitlabhq/issues/2624

See merge request !2044

Fix list with controls display

Introduced in !2025

## Before

![before](/uploads/969f021f1f97062439cc4e836f29bdf6/before.png)

## After

![after](/uploads/defd46ddbd8392625848dfd3ac067869/after.png)
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>


See merge request !2048

Skipped CI because it has already passed. Had to rebase due to CHANGELOG.