Experimental code for naively finding all possible stops

The search space is pretty large and we're heavily limited in the number
of results we can retrieve per request. So we might need to be more
clever.
Be smarter about which stops to look at

We can apparently get a list of "important" stops from the upstream
webservice. Once we have this, it is also easy to get a complete
itinerary for each line.
Merge branch 'stop-scan'