WIP: Fixed tests after implementing a PloneNotificationCenter.
WIP: fix import after implementing a PloneNotificationCenter.
Fixed i18n domain.
Fixed Resource representation.
Reworked Activity attributes:

 - Add new attribute `summary`
 - Adjust title attribute should now store the resources title.
Added Notification Handling to the notification_center.

- get_users_notifications
- mark_notification_as_read
Added first implementation of the notification badge viewlet.

Upgradesteps and some adjustment will follow in separate commits.