Finishing support for custom ringers for event series
-renamed EventLongclickFragment to EventDetailsFragment
-changed sidebar image to be 30% uglier

EventDetailsFragment:
-added calls to database interface to set ringer type for all events in series when saving settings

MainActivity:
-added method getBestRingerForInstance() to return the ringer that should be used for the given event (code duplicate of method from EventSilencerService, this should be moved to a separate class to eliminate duplication)
-added method eventHasCustomRinger() so we know which color to apply to the best ringer

DatabaseInterface:
-added setRingerForAllInstanceOfEvent()  //TODO this could be sped up quite a bit by using an embedded SQL update