Allow center view to handle rotation support

If I want to have more control over which of my view controllers support rotation, it would be nice if the root level drawer controller would delegate to its center view controller.  Since iOS asks for the supported orientations from the root view controller, changing my own view controllers does no good since they are wrapped up inside a drawer controller.  Therefore, I thought it might be a good idea if the drawer controller asked its center view controller for which orientations to support.