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.
Everytime the User check or uncheck a Task Item from the Issue or
Merge Request description, a new update is going to be
added to the activity logs of the Issue or Merge Request.
Note that when using the edit form, you can only update the Task item
status or add/delete/modify existing ones. Doing both actions is not
fully supported.
