use convenient method to check for empty project repo
use NotificationService for handle notify logic when MR created
Use notificationService for MR reassigned
Move new_note email logic to NotificationService
refactor observers. Added BaseObserver with helper methods
refactor observers test since email logic moved to service
stub notification in event model
Merge pull request #3407 from NARKOZ/patch-1

use convenient method to check for empty project repo
annotated
notification scaffold
Prepare UI for notification settings
NotificationService respects disabled notifications now
Add base of Event base
Add base of Notifications
Subscription base
Add notofication state to notifications
Replace Event class with OldEvent class
replace events with old_events
Add new relations with new events system
fix errors