1. Make the "subscribed" text in Issuable sidebar reflect the labels
   subscription status

2. Current user mut be logged-in to toggle issue/MR/label subscription

1. Allow subscribing (the current user) to a label

- Refactor the `Subscription` coffeescript class
  - The main change is that it accepts a container, and conducts all
    DOM queries within its scope. We need this because the labels
    page has multiple instances of `Subscription` on the same page.

2. Creating an issue or MR with labels notifies users subscribed to those labels

- Label `has_many` subscribers through subscriptions.

3. Adding a label to an issue or MR notifies users subscribed to those labels

- This only applies to subscribers of the label that has just been
  added, not all labels for the issue.

The queries that are UNION'd together don't need any eager loading
(since we really only use the resulting SQL instead of having
ActiveRecord actually run the queries). By dropping any eager loaded
associations queries such as the following work instead of producing a
SQL error:

    Project.all.includes(:namespace).search('foo')

This reverts commit 01160fc0, reversing
changes made to 4bff9daf.

- Remove unused Gitlab::Application.routes.url_helpers from Ci::Build
- Remove too much logic from a view, use Ci::Commit.matrix_builds
- Use ci_status_with_icon
- Don't describe symbols

- Remove all view related methods from Ci::Build and CommitStatus
- Remove unused Ci::Commit and Ci::Build methods
- Use polymorphism to render different types of CommitStatus

Also incorporates the review into this, mainly spec changes.

The user has the rights of a public user execpt it can never create a project,
 group, or team. Also it cant view internal projects.

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

It's unclear how these blank values got added, but GitLab.com had a few:

```
irb(main):002:0> Note.where("line_code IS NOT NULL AND line_code = ''").count
=> 439
```

We've added a migration to convert any existing records to use a NULL
value when blank, and updated Note to set blank values to nil before
validation.

The OR condition for source_project_id/target_project_id leads to a
query plan that performs rather poorly on PostgreSQL due to the use of
sub-queries. Because Rails offers no easy alternative for this
particular problem we're forced to using a UNION for both conditions.
The resulting query performs much faster than just using an OR.

This ensures searching namespaces works exactly the same as searching
for any other resource.

Previously this used a regular LIKE which is case-sensitive on
PostgreSQL. This ensures that for both PostgreSQL and MySQL the
searching is case-insensitive similar to searching for projects.

Similar to the changes made to Project.search the method
Project.search_by_title now also uses Arel so it can automatically use
ILIKE/LIKE instead of the lower() function.

This chance is broken up in two steps:

1. Use ILIKE on PostgreSQL and LIKE on MySQL, instead of using
   "WHERE lower(x) LIKE lower(y)" as ILIKE is significantly faster than
   using lower(). In many cases the use of lower() will force a slow
   sequence scan.

2. Instead of using 1 query that searches both projects and namespaces
   using a JOIN we're using 2 separate queries that are UNION'd
   together. Using a JOIN would force a slow sequence scan, using a
   UNION avoids this.

This method now uses Arel as Arel automatically uses ILIKE on PostgreSQL
and LIKE on MySQL, removing the need to handle this manually.

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

This ensures the right caches are flushed when adding a branch via the
UI, instead of only flushing this one random cache.

This ensures Repository#add_tag calls Repository#before_push_tag instead
of just 1 random cache expiration method.

This ensures that Repository#rm_branch calls
before_remove_branch/after_remove_branch instead of just 1 random cache
expiration method.