Allow georeferencing of camera poses into other coordinate systems than UTM

[laxnpander]

Currently, during georeferencing we transform our GNSS measurements from WGS84 into UTM coordinates . It would be nice if we could choose our cartesian coordinate system. So instead of transforming the measurements into UTM we could use EPSG:3857. The rest of the pipeline should be more or less unaffected by the choice of cartesian reference, but it would drastically reduce computational costs during e.g. tileing, because we don't have to rewarp the whole map.