Implement dirtyopts for SubScene scene graph. Currently SubScene only takes into account if its entire scene graph is dirty or not. If it is not dirty, but the SubScene needs to be repainted it will blit the last rendered result (RTT). Else it will render it's graph via root.render(graphics);

Also SubScene implantation uncommented out the method BaseNode.isClean() in order to check if the NG graph is dirty. Please verify correctness.