Support adding to map after map init
Support adding to map after map init

This change supports adding the control to a map via "map.addControl(
L.Control.loading() );" as an alternative method along side the already
supported map options method.
(Includes the concept of hashed loading states.)

DrillingInfo/Leaflet.loading,laurenancona/Leaflet.loading,NBTSolutions/Leaflet.loading,DrillingInfo/Leaflet.loading,NBTSolutions/Leaflet.loading,ebrelsford/Leaflet.loading