Extending support for setting custom ringer for all instances of event series
-replaced EventLongclickActivity with EventLongclickFragment

EventLongclickFragment:
-using DialogFragment instead of activity
-simplified layout to reduce buttons to 'clear' and 'ok'
-reduced size to wrap_content instead of fill_parent
-correctly saves default event ringers to preferences
-TODO still needs to overwrite settings for all instances in the local database

DatabaseInterface:
-added error checking to setRingerType() (fixes #9)

Prefs:
-added methods to store/retrieve map of Integer->Integer to/from shared preferences
-added getRingerForEventSeries() to return saved ringer for a series of event instances
-added setRingerForEventSeries() to store a specific ringer for an event series
-added unsetRingerTypeForEventSeries() to clear saved ringer for the given event series

EventSilencerService:
-getBestRingerType() now prioritizes ringers as: generic default ringer < calendar specific ringer < event series ringer < instance ringer (calender support not yet added