Basic support for per calendar ringer settings
SelectCalendarsActivity:
-fixed onItemClickListener() not working on calendar listview
-fixed calenders in the listview being clickable even if all calendars are set to be synced
-implemented AlertDialog to select ringer for specific calendars

MainActivity:
-updated getRingerIcon() to return a colorized icon to show whether ringer state is from default settings (ugly red), event series settings (ugly green), calendar settings (ugly blue), or event instance settings (basic grey)
-icons still not reflecting colors from event series properly, likely due to all database rows of event series being updated with new event ringer type (this should only be stored in preferences)
Bugfixes
EventSilencerService:
-now properly includes calendar and event series settings when determining whether an event should be ignored
-now properly finds the best ringer to use (default < calendar < event series < event instance) fixes #13

EventDetailsFragment:
-applying a ringer to an event series now removes all custom ringers from the local database before writing to preferences, fixes #14
-slightly better layout (more padding, adding icons to event title and calendar name
-checkbox to save setting for all instances only visible if there are more than one instance of the event
-clear button only visible if the event instance has a custom ringer or if the event series has a custom ringer set

Columns, DatabaseInterface, EventDatabaseOpenHelper, SimpleCalendarEvent:
-removed logic for custom ringer.  Events now only store their specific instance ringer, preferences must be queried to determine whether a calendar or event series specific ringer has been applied

build.gradle, Versioning:
-debug builds now clearly marked as pre-release debug builds (with build date)