'Gets back a previously saved action. This method can return None if the action
was saved since too much time (this case should be handled in a smart way).
:param key: The key given by save_session_action()
:type key: integer
:return: The saved action or None.
:rtype: anything'

@http.route('/web/session/get_session_action', type='json', auth='user')
def get_session_action(self, key):

    return request.session.get_action(key)
