Add basic front with map & markers

[amwolff]

I think this looks good enough on mobiles: https://leafletjs.com/examples/mobile/. It also doesn't require too much logic in the frontend code. Added markers would be the vehicles. Later we can add custom icons for them with additional information on top of them.

For the map tiles I think we can use the MapServer service from https://msipmo.olsztyn.eu/imap/. One thing I'm afraid of is it requires some token policy and I don't know if we can handle that (legally).