Merge branch '12743-subscribe-to-label' into 'master'

Allow subscribing to labels

This implement #12743 and supersedes !2799 (thanks @timothyandrew!).

- Subscribe (and unsubscribe) for labels
- When an issue/merge request is created, notify all subscribers of all its labels
- When an issue/merge request is edited, notify all subscribers of all its newly-added labels

## Done

- [x] Verify that a user is signed in to subscribe/unsubscribe from a label.
- [x] Merge conflicts
- [x] Integration tests
- [x] `issuable.subscribed?` should check subscribers and participants
- [x] When an issuable is relabeled, notify subscribers of the *newly added* labels only
- [x] Screenshots:

### Labels page

![Screen_Shot_2016-03-07_at_19.05.44](/uploads/3e69064e9e1a06ee2e27c778776c1407/Screen_Shot_2016-03-07_at_19.05.44.png)

### HTML email

![Screen_Shot_2016-03-07_at_19.07.36](/uploads/e484e06366a738385f1f6d71b52eecf7/Screen_Shot_2016-03-07_at_19.07.36.png)

### Plain text email

![Screen_Shot_2016-03-07_at_19.07.50](/uploads/dc05f710a8f7ab5eae9f72aa2110e741/Screen_Shot_2016-03-07_at_19.07.50.png)

PS: I've set the milestone to 8.6 since it's getting late for 8.5...

See merge request !3115

1 files changed, 1 insertions, 0 deletions

diff --git a/CHANGELOG b/CHANGELOG
index ebf49cd2ac0..7f076f70c7c 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -28,6 +28,7 @@ v 8.6.0 (unreleased)
   - Update documentation to reflect Guest role not being enforced on internal projects
   - Allow search for logged out users
   - Allow to define on which builds the current one depends on
+  - Allow user subscription to a label: get notified for issues/merge requests related to that label (Timothy Andrew)
   - Fix bug where Bitbucket `closed` issues were imported as `opened` (Iuri de Silvio)
   - Don't show Issues/MRs from archived projects in Groups view
   - Fix wrong "iid of max iid" in Issuable sidebar for some merged MRs