Set a value for a specified custom field
        field_name - Name of the custom field you want.
        value - Value to set it to

def set_custom_value(self, field_name, value):
        """ Set a value for a specified custom field
        field_name - Name of the custom field you want.
        value - Value to set it to
        """
        custom_field = self.get_custom_field(field_name)
        custom_value = CustomFieldValue.objects.get_or_create(
            field=custom_field, object_id=self.id)[0]
        custom_value.value = value
        custom_value.save()