[x] backend: add new API endpoint that only gets [trip, spot, single_pitch_route, multi_pitch_route, pitch, ascent]-ids and last changed datetime
[x] backend: add new API endpoint that gets all [trip, spot, single_pitch_route, multi_pitch_route, pitch, ascent] of a given List of ids
[x] frontend: when a get Request, e.g. getTrips(), is sent, first only do getTripIds(), check whether those are in cache and if not request them seperatly