Create a proxy for a widget and add it to this group

        :param name: The name or key of the proxy, which will be emitted with
                     the changed signal
        :param widget: The widget to create a proxy for

def add_proxy_for(self, name, widget):
        """Create a proxy for a widget and add it to this group

        :param name: The name or key of the proxy, which will be emitted with
                     the changed signal
        :param widget: The widget to create a proxy for
        """
        proxy = proxy_for(widget)
        self.add_proxy(name, proxy)