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

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

Update build log incrementally

Proof of concept implementation of incremental sending of build log to browser.

cc @jschatz1 @vsizov @grzesiek @tmaczukin 


See merge request !3737

Updated CHANGELOG for 8.7.5

See merge request !4129

Only show forks for users who can download code

The ForksController enforces this, so don't show the link if it won't go anywhere.

Closes #14272.

See merge request !4017

[ci skip]

and drop exception handling around HealthCheck::Utils.process_checks, it wasn't needed