@Override
    public void cleanup() {
        viewPort.detachScene(rootNode);
        super.cleanup();
    }
Creates the AppState with the given unique ID, ViewPort, and root Node, attaches
the root Node to the ViewPort and updates it.

@param id the desired AppState ID
@param viewPort An existing ViewPort
@param rootNode An existing root Node
jme3-core/src/main/java/com/jme3/app/state/RootNodeAppState.java