Extensions to ws/transit/ API

Changes in /ws/API:
* add new method /ws/transit/calendar to retrieve information from calendar.txt and calendardates.txt GTFS files
* extend trips tags in <RouteData><variant>..</></> by information about trip headsign, calendar Id and number of trips for given variant anf calendar Id. i.e. < trip agency="5_1_6689_2" id="1" calendarId="2" numberOfTrips="4" headsign="KÓRNICKA"/> 
* refactoring of some classes