Created helper class to hide content in issue sidebar when collapsed

Closes#13764
See merge request !2968
Refactor html/css for lists and improve help UI page
* dry lists html/css removing a lot of style duplicates
* fix snippets list to match common style
* fix extra bottom margin for groups list
* improve help page ui so it looks clean
Fixes#11873
See merge request !2977
Move "I should see Crowd login form" feature to a view spec
We were doing all kinds of code gymnastics to "enable" Crowd in the
feature spec and this would sometimes cause a transient failure.
Really what it's testing is if the Crowd login form shows when Crowd's
enabled, so this is much better suited to a view spec.
See merge request !2963
Sidebar overlaps content when screen is below 1200px.
When screen is below 1200px, the sidebar overlaps.
When screen is above 1200px, the sidebar pushes content out.
z-index change to make sure hamburger stays on top.
Fixes#12717


Also sorry I couldn't get the collapse button in the screen cap. It's there.
See merge request !2620
We were doing all kinds of code gymnastics to "enable" Crowd in the
feature spec and this would sometimes cause a transient failure.
Really what it's testing is if the Crowd login form shows when Crowd's
enabled, so this is much better suited to a view spec.
Improve the formatting for the user page bio
Resolves#13406.
Problems, per the Issue above:
- The bio has an extra period appended by the HAML view.
- The bio isn't given its own line, not differentiated from username and account creation date.
- The bio is allowed to span almost the full width of the container, would probably look better if it were only allowed a max width of something like 750px.
This commit:
- Separates the User page bio from the username and account creation
date.
- Separates the pseudo-selector adding a Middle Dot out from the
`profile-link-holder` class and into a `middle-dot-divider` class.
Before:

With this Merge Request:

See merge request !2827
Changed padding & background color for highlighted notes
Closes#12453

See merge request !2937
Fix group projects styles
Makes new project button visible when no projects are available.
Fixes#13193
# BEFORE

# AFTER (w/projects)

# AFTER (no projects)

cc @creamzy @skyruler
See merge request !2714
- Separates the User page bio from the username and account creation
date.
- Separates the pseudo-selector adding a Middle Dot out from the
`profile-link-holder` class and into a `middle-dot-divider` class.
Resolves#13406.
See merge request !2827.