Adds menus to itself, required by ViewBox

def copy(self):
        """Adds menus to itself, required by ViewBox"""
        # copied from pyqtgraph ViewBoxMenu
        m = QtGui.QMenu()
        for sm in self.subMenus():
            if isinstance(sm, QtGui.QMenu):
                m.addMenu(sm)
            else:
                m.addAction(sm)
        m.setTitle(self.title())
        return m