Start work on the message_thread observer, and test increased privacy levels.
Refactor the message_thread subscribe_users functionality into a separate class.
Use new ThreadSubscriber worker - it's a state change, not a notification.
Add reminders that notifications need sending too.
Refactor.
Confirm remaining subscription behaviour.
Thread subscription behaviour when changing the thread issue.
Add reminder of that group changes need handling too.
Add subscription changes for when a user joins a group.
Ensure members are unsubscribed from private threads when they leave a group.
Add a UserLocation observer, and subscribe to relevant issue threads when created or saved.
Merge branch 'staging' into observers

Conflicts:
	app/controllers/group/message_threads_controller.rb
	app/controllers/issue/message_threads_controller.rb
	app/controllers/message_threads_controller.rb
Add stub UserPref observer.
Rubocop fixes.
More quoting fixes and remove unused variable.
When you change your pref regarding group admin discussions, subscribe to the relevant threads.
Unsubscribe from threads when you no longer wish to participate in group admin discussions.
subscribe to existing group threads when you start subscribing to new ones
Unsubscribe from group threads when unticking the box - but be cautious around issues that are also in user locations.
Subscribe and unsubscribe from threads when changing user locations preference.