Change render system for the DebugDraw item to scene graph

I've tried to turn the `DebugDraw` render system to use Scene graph.
Since I am newbie in GL painting all advices are appreciated!
As for me, I'm worried about recreating `oldNode` in `Box2DDebugDraw::updatePaintNode` instead of updating its geometry. But I have no idea at all how to link geometry data passed by Box2D to GL node. So I delete the node tree and recreate it each time step.