Added gcm-server dependency
notifications: added google api key
notifications: added basic NotificationRouter
notifications: ClientDatastore sorts by source instead of client
notifications: added NotificationSender
test: added ClientDatastoreTest
grabber: PegelOnlineGrabber includes characteristic values
data: added final fields to AllowedValueTypes for easier access
notifications: added debug router for viewing registered clients
notifications: cleanup in NotificationSender
notifications: NotificationRouter can send test gcm msgs