Made the Bing base layer optional (by factoring out the Bing API key) and added the unlabeled Bing Aerial as another base layer; added on-map attribution for the OSM Mapnik and MapQuest base layers
Made the Bing base layer optional (by factoring out the Bing API key) and added the unlabeled Bing Aerial as another base layer; added on-map attribution for the OSM Mapnik and MapQuest base layers

OSMPH/Imagery_Coverage_Map,OSMPH/Imagery_Coverage_Map