convert button model types to use emitter, https://github.com/phetsims/axon/issues/180 https://github.com/phetsims/sun/issues/340
convert button model types to use emitter, https://github.com/phetsims/axon/issues/180 https://github.com/phetsims/sun/issues/340

phetsims/tandem,phetsims/tandem,phetsims/tandem