[Enhancement] #33 Add IGN Geoportail and GMap geocoding - funded by Pays de Pontivy

The administrator must be able to choose the geocoder that he would like the web user will use.

The OpenStreetMap geocoder, Nominatom, may already be selected.
The GMap geocoder has to be used with Google baselayer to respect the CGU.
The IGN Géoportail geocoder is for french users.