Fix bug where projects would appear to be stuck in the forked import state

A race condition existed between when Rails committed the `import_status` to
`started` and when the Sidekiq worker forked a project. If this fork were quick,
it's possible that the worker would attempt to move into the `finished` state
before the `started` state took effect.

As mentioned in https://github.com/mperham/sidekiq/wiki/Problems-and-Troubleshooting#cannot-find-modelname-with-id12345,
we can either delay the worker to ensure the DB has a chance to update, or use the nice `after_commit_queue` gem to schedule the task after the state machine commit. See:

* https://github.com/pluginaweek/state_machine/issues/191 
* https://github.com/shellycloud/after_commit_queue


Closes #2736

See merge request !1434

Fix Slack notification URL and remove the usage of Ci::RoutesHelper

Fix for #2644

See merge request !1391

[ci skip]

Make instructions for CI disable checkbox clear.

Fix confusion in https://gitlab.com/gitlab-org/gitlab-ce/issues/2663

See merge request !1431

[ci skip]

Add missing path change back

Get CI token from ci projects

This fixes problem when GitLabCiService had different token than stored
in Ci::Project.

See merge request !1425

Update mailroom to 0.5.2

Fixes #2698 and #2711.

See merge request !1424

This allows us to see a breakdown of API requests in New Relic.

Add Troubleshooting section to 8.0 docs

[ci skip]

See merge request !1416

Help page improvements

- Only signed-in users can see version information
- Add "Community Edition" text so the header is
  less barren when version information is hidden
- Minor copy edits
- Make all "Quick help" link text the entire body
  of the link. Prior, it wasn't obvious which part
  of each item was an actual link.

Closes #2721 

See merge request !1415

Closes #2585

Closes https://github.com/gitlabhq/gitlabhq/issues/9657

Closes #2702

[ci skip]

[ci skip]

Fix top margin for sign-in button on public pages

Closes #2615

[ci skip]

See merge request !1412

[ci skip]

Closes #2653

Prevent double-prefixing of help page paths

Closes #2679 

See merge request !1400

This was causing the task `gitlab-rake gitlab:incoming_email:check`
to fail.

[ci skip]

8.0.0 is released; add 8.0.1 entry to CHANGELOG

[ci skip]

See merge request !1394

[ci skip]

Add to migration on what to do if you don't want your data.

If you don't want to migrate your CI data , remove the old builds directory.

See merge request !1392

Add to migration on what to do if you don't want your data.

If you don't want to migrate your CI data , remove the old builds directory.

See merge request !1392

Mention Reply by email in installation doc.

Added the "Enable Reply by email" section and moved the others around.

See merge request !1390

Ci migration doc improvements

Use export improvements in CI 8.0.1, make upgrades a more prominent part of the process, do not shut down GitLab during CI data import.

See merge request !1387

Ci migration doc improvements

Use export improvements in CI 8.0.1, make upgrades a more prominent part of the process, do not shut down GitLab during CI data import.

See merge request !1387