Update TimetableAccessor, accessor types, add DepartureTime enumerable

- New AccessorType enumerable for the coming GTFS accessor, renamed
other enumerables (now all end with ...Accessor)
- Require a pointer to the used TimetableAccessorInfo object in the
TimetableAccessor constructor, because it's always needed and would
actually crash if it is not set by derived classes
- Remove return values from TimetableAccessor::requestXXX functions,
not needed and the GTFS accessor will work without network requests,
therefore it will not create a KIO::StoredTransferJob.
Make these functions virtual, so that derived classes can do
something else than download a document
- DepartureHour/DepartureMinute values are used to create a
DepartureTime value, if it is not available
(same for ArrivalHour/ArrivalMinute)
- DepartureTime, ArrivalTime can be used with second information
- Will be used for GTFS, which can include seconds in time values
- Used by the XML accessor (de_rmv), to store the time as QTime object,
but without seconds
- Update DepartureInfo/JourneyInfo::generateHash functions in
libpublictransporthelper to include seconds