public void RemoveContentController(ContentTypeController controller)
        {
            controller.ContentOpened -= ControllerContentOpenedHandler;
            controller.ContentClosed -= ControllerContentClosedHandler;

            _contentControllers.Remove(controller);
        }
        public void AddContentController(ContentTypeController controller)
        {
            controller.ContentOpened += ControllerContentOpenedHandler;
            controller.ContentClosed += ControllerContentClosedHandler;

            _contentControllers.Add(controller);
        }