Add a config option to prefer entrances defined in GTFS stops.txt (location_type=2) instead of those inferred from OSM. If no such GTFS entrances are present for a station, fall back to OSM as usual.

This allows better control in cases where GTFS provides more accurate entrance data than OSM.

Example:

In the Warsaw GTFS feed, the metro station Dworzec Wileński includes all station entrances precisely as location_type=2 stops:

However, OSM either lacks metro entrances entirely or they are mis-mapped, causing MOTIS to not recognize any entrances at all. Using the GTFS-defined entrances ensures correct pedestrian routing in such cases.