Callback to go to the next tab. Called by the accel key.

def accel_next(self, *args):
        """Callback to go to the next tab. Called by the accel key.
        """
        if self.get_notebook().get_current_page() + 1 == self.get_notebook().get_n_pages():
            self.get_notebook().set_current_page(0)
        else:
            self.get_notebook().next_page()
        return True