Return a list of custom fields for this model, directly callable
        without an instance. Use like Foo.get_model_custom_fields(Foo)

def get_model_custom_fields(self):
        """ Return a list of custom fields for this model, directly callable
        without an instance. Use like Foo.get_model_custom_fields(Foo)
        """
        return CustomField.objects.filter(
            content_type=ContentType.objects.get_for_model(self))