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