Implement comments on parallel diff

Fixes #1565

See merge request !1090

Fix grammatical error in 'not merged changes' msg

Update user_management.md

Adding ability to configure webhook timeout via gitlab.yml

[Refactor] Remove duplicated labels step

formatting changes, table->database

Use the default Unicorn socket backlog value: 1024

See merge request !1087

set fail_timeout=0 as recommended by Unicorn

[UX] Disable buttons if form is empty

[UX] Update tag count if tag gets deleted via web interface

set the number of workers to # of cores

Add Feedback link

Set's fail_timeout=0 as recommended by
http://unicorn.bogomips.org/Unicorn/Configurator.html#method-i-timeout
when Unicorn is running behind nginx.

Add requests link for feature requests.

Make formatting consistent on page.

Change table -> database as they are database permissions.

Zen Mode for issues/MR/notes

Fix serialize migration

Close Zen mode by ESC, foward/backward

update grant command to match how mysql shows

Feature oauth refactoring

Only use class methods when needed. In addition, make a proper extension of Gitlab::Oauth::User.

See merge request !1062

Clickable labels

When I open issue with label `Ready for Merge` I usually want to see more issues with this label. I should visit project issues page and click on such label to see issues filtered. With this MR labels are clickable so you can get in one click from Issue show page to all issues with same labels

See merge request !1085