- moved stoptime related functionality into new core:data:stoptime module
- will feature all the different realtime stoptime sources to be
integrated later
- create proper database schema for future migrations
- deduplicate trips into stoppingpatterns, since many trips share the
exact same stopping pattern
- stoptimes are now linked to stoppingpatterns instead
- stoppingpattern ids are generated from a hash composed of all stoptimes
- stoptimes now use deltas for arrival time to save space
