calendar table rework:
calendar table rework:

 - by default more hard-coded calendars are provided
 - holidays are added correctly, if data to import spans multiple years
 - not everything is added in the calendar_dates table... now a simple
mechanism is used that tries to store as much as possible in the
calendar table and only use calendar_dates when necessary
stkdiretto/diva2gtfs,stkdiretto/diva2gtfs,nikolauskrismer/diva2gtfs,nikolauskrismer/diva2gtfs