Activity: Ignore activities actor when generating notifications for all watchers.
Activity: fixed typo in `Activity.notify` method.
Activity: Added `only_unread` parameter for the `get_current_users_notifications` method.
Pep8 cleanup (Task.test_notifications).
WIP: Fixed `only_unread` parameter query.
Added Notfication badge viewlet:

 - Includes Badge Icon viewlet, wich shows unread notifications.
 - A view to mark notification as read.