Closes #44

Work in progress. Only status is documented at the moment.

Select top station on work days (Mo .. Fr) with arrival < 13:00 or
departure >= 13:00.

order is ascending by default, resulting in flop instead of top destinations.

Until now, tripIDs were cached based on station and departure timestamp.
These are identical for any two trains departing at the same time at the same
station, leading to one of those getting being assigned a wrong tripID.

From now on, only the JSON reported by transport.rest is cached -- tripIDs
are always recomputed based on it.