Sets whether or not the user should be able to close this overlay widget.

        :param      state | <bool>

def setClosable(self, state):
        """
        Sets whether or not the user should be able to close this overlay widget.

        :param      state | <bool>
        """
        self._closable = state
        if state:
            self._closeButton.show()
        else:
            self._closeButton.hide()