- turned rootview into opengl widget
- made gameview/background/particleview objects instead of widgets because qt opengl stuff doesn't supported nested widgets
- made rootview forward the paintevent to those ^ sub widgets/objects
- disabled parallel rendering by default because it will not be supported now anymore
- embedded game view inside qml because there seems to be no other way of implementing opengl drawing + qml (because of how the opengl context is managed)
- made main menu and game work with opengl for now with some hacks, disabled hud because it needs to be embedded in the exiting qml first instead of being a separate view