renamed parameter
don't pass entire model to AttachDetachToggleButtons
don't pass entire model to BackgroundNode
don't pass entire model to BarGraphNode
don't pass entire model to FrictionControl
don't pass the entire model to GridNode
don't pass entire model to MassSlider
don't pass entire model to PieChartLegend
don't pass entire model to PieChartNode
don't pass entire model to PlaybackSpeedControl
don't pass entire model to SkaterNode