Formats the self.filtered_data in a way suitable for a formset.

def _get_formset_data(self):
        """Formats the self.filtered_data in a way suitable for a formset."""
        data = []
        for datum in self.filtered_data:
            form_data = {}
            for column in self.columns.values():
                value = column.get_data(datum)
                form_data[column.name] = value
            form_data['id'] = self.get_object_id(datum)
            data.append(form_data)
        return data