Document cluster position behavior

(cherry picked from commit 5d6f3e796069c5b62a79c75e0f6b1de3afb56291)
Add station_number property to Station class

A station_number can be given (optional) when adding a station to a
cluster.
If no number is given the station_id will be used for the
station_number.
Add a function to get a station based on station_number.
station_id is now 0-based, for consistency.

(cherry picked from commit acdffa7923603a09bcca872982fe30b20d89edfb)
Refactor ScienceParkCluster

Add warning when it can not connect to Public Database,
in which case it will use hard coded values.
Also add station 508 to the default set of stations.

(cherry picked from commit 2ea89d5794e2c5588aa4f63bd3e595669a27fff5)
Merge branch 'fix-slow-import'

Before this 'fix', we had a startup time of over 5 minutes on our brand
new Pique installation.  Sigh.