Rewrote the home button to use PushButton, see https://github.com/phetsims/joist/issues/90
Made highlight extend scenery.Node, see https://github.com/phetsims/joist/issues/92
Simplified use of highlight node, see https://github.com/phetsims/joist/issues/92
Made it possible to invert the highlights, see https://github.com/phetsims/joist/issues/78
Moved HomeButton from scenery-phet to joist