Do what `RequestHandler.get_secure_cookie` does(when `value` is not None),
        but with a more friendly name

        What opposite to it is `RequestHandler.create_signed_value`

def decode_signed_value(self, name, value, max_age_days=None):
        """Do what `RequestHandler.get_secure_cookie` does(when `value` is not None),
        but with a more friendly name

        What opposite to it is `RequestHandler.create_signed_value`
        """
        kwgs = {}
        if max_age_days is not None:
            kwgs['max_age_days'] = max_age_days
        return tornado.web.decode_signed_value(settings['COOKIE_SECRET'], name, value, **kwgs)