[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
Merge pull request #9 from subugoe/geopicker

[ADWD-1193] Added layer switcher to geopicker