Add a factor to the workflow

        :param factor: The factor object
        :type factor: Factor | MultiOutputFactor | NodeCreationFactor
        :return: None

def _add_factor(self, factor):
        """
        Add a factor to the workflow

        :param factor: The factor object
        :type factor: Factor | MultiOutputFactor | NodeCreationFactor
        :return: None
        """
        self.factors.append(factor)
        logging.info("Added factor with tool {} ".format(factor.tool))