[ADWD-1193] Added layer switcher to geopicker

Included layers are:
* Mapbox (unchanged)
* OpenStreetMap (natively supported by Leaflet)
* Google Maps Streets (via plugin)
* Google Maps Satellite (dito)

Removed close button as the map closes when losing focus

Please check if the Google license permits embedding of its proprietary maps JS or if it has to be loaded directly from Google.