improve response precision based on IP

[karussell]

In photon we will have a better location bias komoot/photon#580 once it is deployed.

With that and the free geo DB from maxmind: https://github.com/maxmind/GeoIP2-java (using the offline database) we could improve search precision if users want that. E.g. an additional parameter ip=<ip> or header_for_ip=X-Forwarded-For.