gravity-and-orbits: new image loading implementation
Merge branch 'master' of https://github.com/phetsims/gravity-and-orbits

Conflicts:
	js/gravity-and-orbits-config.js
	js/view/BottomControlPanel/SpeedPushButtons/PlayPauseButton.js
	js/view/ResetAllButton.js
	js/view/RightControlPanel/MassMenu/Slider/Slider.js
	js/view/RightControlPanel/PlanetModeMenu/PlanetModeResetButton.js
	js/view/RightControlPanel/SpaceObjectsPropertyCheckbox/SpaceObjectsPropertyCheckbox.js
	js/view/SpaceObject/Earth.js
	js/view/SpaceObject/Moon.js
	js/view/SpaceObject/SpaceStation.js
	js/view/ViewModePanel/ViewModePanel.js