Refactor diff notes

Related to https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4101

/cc @rspeicher 

See merge request !4110

Change all occurrences of doc.gitlab.com to docs.gitlab.com

Now that https://gitlab.com/gitlab-com/operations/issues/233 kicked in.

See merge request !4148

[ci skip]

Revert "Merge branch 'doc-fix-db-gem-install-instructions' into 'master'"

This reverts commit 66d8ef1a, reversing
changes made to 6a8359f3.

The `--with` option was added in Bundler 1.10 but in this case it
shouldn't even be needed: I've tested the original command locally and
the pg gem was installed, so I believe the user that opened the original
MR ran the wrong command (i.e. `sudo -u git -H bundle install --without
development test postgres --deployment` instead of `sudo -u git -H bundle
install --without development test mysql --deployment`.

See discussion at
https://gitlab.com/gitlab-org/gitlab-ce/commit/66d8ef1ad9d5952b7e7f026658f71aafc861950e
for more context.

See merge request !4144

Remove activerecord-deprecated_finders gem

We don’t use any of the deprecated finders, so it should be safe to remove.

See https://github.com/rails/activerecord-deprecated_finders#active-record-deprecated-finders for more information.

Resolves #17015.

See merge request !3981

Rubocop: require space round operators

This enables rubocop to require space around opertators and fix offenses in the codebase.
There is another merge-request to solve remaining offenses in EE codebase, merge it first: gitlab-org/gitlab-ee!388

Fixes #17398 

See merge request !4112

Reduce width of side nav

Closes #17338    
Part of #14838    
Left: old; Right: new    
<img src="/uploads/7dba5f22d6bdf1249bab5166addb25b5/Screen_Shot_2016-05-10_at_4.34.07_PM.png" width="500px">

See merge request !4109

Fix mobile dropdown bug

Closes #17501     
![dropdown](/uploads/d0cc6d9472bd8aa1aaf392d5c4eb3791/dropdown.gif)



See merge request !4142

Fix UI issues caused by header height decrease to 50px

- fix blank spacing for issue sidebar
- fix login btn alignment for non logged in users

See merge request !4143

Add UI changes in 8.8 to changelog

For !3824 and !3980

[ci skip]

See merge request !4140

This reverts commit 66d8ef1a, reversing
changes made to 6a8359f3.

The `--with` option was added in Bundler 1.10 but in this case it
shouldn't even be needed: I've tested the original command locally and
the pg gem was installed, so I believe the user that opened the original
MR ran the wrong command (i.e. `sudo -u git -H bundle install --without
development test postgres --deployment` instead of `sudo -u git -H bundle
install --without development test mysql --deployment`.

See discussion at
https://gitlab.com/gitlab-org/gitlab-ce/commit/66d8ef1ad9d5952b7e7f026658f71aafc861950e
for more context.

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

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

Remove background color differentiation from gitlab logo/text in sidebar
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

cc @annabeldunstone @skyruler 

See merge request !4139

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

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

Move broadcast msg into content-wrapper

Closes #17485  

<img src="/uploads/ab365f471209c55d2ee876cf558d4032/Screen_Shot_2016-05-12_at_4.21.22_PM.png" width="800px">

See merge request !4132

Fix minor typos in admin health check page

Fix minor typos from gitlab-org/gitlab-ce!3888

cc/ @DouweM @twk3 

See merge request !4134

Clean up EventsHelper spec

Extracted from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4090

See merge request !4133

Enable the Rubocop DeprecatedClassMethods cop

This reports uses of `File.exists?` and `Dir.exists?`, which were both
deprecated in Ruby and will eventually be removed in favor of `.exist?`.
Also fixes all existing uses of the deprecated methods.

See merge request !4087

Fix a description for default scope on builds

Should be "**All* builds (from this project)" for the {project,admin}
builds page without scope.

Fix a regression on !2243 (#4240).

See merge request !4118

Add API endpoints for un/subscribing from/to a label



See merge request !4051

# Conflicts:
#	db/schema.rb

Closes #15638