Persistent notifications

closes #3057
- add Notification model
- update injected Notifications object to handle persistent notifications
- load server notifications on setup if logged in otherwise on successful sign-in
- changed all notifications.closeAll calls to closePassive
- close all notifications on sign out

Known issues:
- Needs tests
- The check for a logged in user in the 'loadServerNotifications' action will need updating once #3060 lands
Is this property something inspired by a server side model? Doesn't look like it's ever used otherwise; ditto `location`