convert GQ to use SCENERY_PHET/BackgroundNode, https://github.com/phetsims/graphing-quadratics/issues/135
convert GQ to use SCENERY_PHET/BackgroundNode, https://github.com/phetsims/graphing-quadratics/issues/135

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