Adding counting of listeners so we don't add duplicate listeners to Property, see https://github.com/phetsims/scenery/issues/660 and https://github.com/phetsims/axon/issues/129
Adding counting of listeners so we don't add duplicate listeners to Property, see https://github.com/phetsims/scenery/issues/660 and https://github.com/phetsims/axon/issues/129

phetsims/scenery,phetsims/scenery,phetsims/scenery