Background process note logic for #3948

Quick and dirty way to get *most* of the note processing out of band and into the background. Seeing some pretty nice speed bumps. Keep in mind that doing this in process results in slower and slower responses as more notes are added and more participants exist.

```
without background processing
  Completed 200 OK in 627ms (Views: 0.5ms | ActiveRecord: 32.3ms)
  Completed 200 OK in 478ms (Views: 0.8ms | ActiveRecord: 28.3ms)
  Completed 200 OK in 1107ms (Views: 0.6ms | ActiveRecord: 36.6ms)

with background processing
  Completed 200 OK in 108ms (Views: 0.6ms | ActiveRecord: 4.7ms)
  Completed 200 OK in 78ms (Views: 0.5ms | ActiveRecord: 4.5ms)
  Completed 200 OK in 164ms (Views: 0.5ms | ActiveRecord: 8.3ms)
```

As you can see, speeds are consistent when doing the harder work out of process. I'm not sure the number of sql queries we're saving, but based on the logs alone it's a pretty good amount.

@dzaporozhets @yorickpeterse I would love some input on this.

See merge request !2631

Partially revert "Add IP check against DNSBLs at account sign-up"

This partially reverts 6a5cd3ca - we keep the migration and add a new
migration that reverts it in order to keep migration history intact.

See merge request !2643

Prevent transient Capybara timeouts during feature tests

The problem occurred because asset compilation takes a long time, so
when the asset cache didn't exist and the first test ran, it would often
(randomly) time out during the generation before the actual test even
had a chance to run.

Now we check if the cache exists before the suite runs, and if not, we
manually fire a request to the root URL in order to generate it. This
should allow subsequent tests to use the cached assets.

See merge request !2646

Revert "Revert "Remove the `:coffee` and `:coffeescript` Haml filters""

This reverts commit b0145d76.

See merge request !2642

fix syntax error on 2.1 and rubocop on 2.2

Background:

Hashes `{:'key': 'value'}` are not valid in 2.1 but are recommended by Rubocop on 2.2. We only use those when we have a key such as `weird-key`, `weird.key`, etc... 

We could disable Rubocop but it wouldn't warn us about the recommended syntax since `Ruby 1.9`: `{key: 'value'}`, which is valid for `Ruby 1.9+`.

Workaround 1 could be disabling `Style/HashSyntax:` in `rubocop.yml`. 

Workaround 2 (tried in this MR) is to trick Rubocop using `.to_sym` which is effectively the same as adding the `:`. This would allow to keep the warning in place.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/12801

See merge request !2637

The problem occurred because asset compilation takes a long time, so
when the asset cache didn't exist and the first test ran, it would often
(randomly) time out during the generation before the actual test even
had a chance to run.

Now we check if the cache exists before the suite runs, and if not, we
manually fire a request to the root URL in order to generate it. This
should allow subsequent tests to use the cached assets.

This partially reverts 6a5cd3ca - we keep the migration and add a new
migration that reverts it in order to keep migration history intact.

Correctly determine MR diff base when MR has merge conflicts

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/12779

See merge request !2632

Fix highlighting in blame view.

See merge request !2630

This reverts commit b0145d76.

Backport LDAP user assignment changes from EE

See https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/146

See merge request !2641

Update sentry-raven gem.

Should resolve `fatal: Not a git repository (or any of the parent directories): .git` warnings.

Fixes #12657

See merge request !2636

See https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/146

Show list of forks for a given Project

Closes #2406

See merge request !2376

Save list sort in a cookie

Closes #5546 

See merge request !2537

Fix preventing migration from crashing in very specific cases

Closes #12606. Closes #12501.

/cc @yorickpeterse @dbalexandre 

See merge request !2600

Improve consistency and duplication for Merge Request API

* Follow REST for merge request API route
* Remove repeating comments API for MR
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fixes #4759 and #11810 

See merge request !2639

Removed sorted text from dropdowns

![Screen_Shot_2016-01-28_at_09.04.36](/uploads/9e0e1fdb45ad12d122f860a2164d9396/Screen_Shot_2016-01-28_at_09.04.36.png)

Closes #12796 

cc @creamzy @jschatz1 

See merge request !2635

* Follow REST for merge request API route
* Remove repeating comments API for MR
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Makes ol margin big enough for 3 digits.

Fixes #7960 

![Screen_Shot_2016-01-25_at_11.20.03_PM](/uploads/73c4b9e939fe108fb3b8221e16e686bd/Screen_Shot_2016-01-25_at_11.20.03_PM.png)


See merge request !2608

Adds feature: Ajax Close/Open updates discussion automatically

Triggers jQuery event <br/>
Fixes #5544

See merge request !2610

This ensures that rake tasks that don't need a DB connection can be run
without one.

Return a fake application settings OpenStruct when this is not the case.
Also, use ActiveRecord::Base.connection_pool.active_connection? instead
of ActiveRecord::Base.connection.active? to avoid driver exception.

Closes #12796

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