Speed-Up queries by better look-ups / reachable trips

[MoKob]

Our current queries do a lot of linear look-ups on trips. We can speed-up our queries quite immensely by adding look-ups to the stop-tables. These should allow finding the correct stop by it's ID within the table, instead of searching linearly over all trips.

In addition, we currently only reach stops. But we can skip over looking at entire trips by remembering which trips we already reached. A trip cannot improve any result, if we reached it at the same (or earlier) departure (base station) on an earlier stop. If we only reached it at the same departure, but a later stop, we can limit our search to the stations up to the stop we already reached. This would allow us to scan each trip only once per departure.