Avoid BASE_URL & PLAN_APP_INFO being mutated after map is created

Previously setting PLAN_APP_INFO after creating a map could
inadvertently alter the previously created maps info due to popUp
referencing the global HubMap.PLAN_APP_INFO and the fact that popUp is
not called until the features have loaded.
Add Leaflet.MarkerCluster to avoid a rash of markers
Add license file and make package.json valid