This speeds up the map significantly and makes coordinates_by_station obsolete

This increases resilience against EVA ID reuse

(copy-paste error)

Closes #146

Closes #144

this avoids a race condition when the worker requests all current checkins and
takes a while before getting to update the data

Closes #143

This is in preparation for supporting multiple HAFAS backends, and possibly
EFA and RIS::Journeys.