implemented "Down. Rub fast or slow."; refactored MovementDescriber to by default have a bottom edge alert https://github.com/phetsims/friction/issues/124
implemented "Down. Rub fast or slow."; refactored MovementDescriber to by default have a bottom edge alert https://github.com/phetsims/friction/issues/124

phetsims/scenery-phet,phetsims/scenery-phet,phetsims/scenery-phet