Relabel images by moving from parent dir with old label `class_old` to parent dir with new label `class_new`.

def relabel(self, change):
        "Relabel images by moving from parent dir with old label `class_old` to parent dir with new label `class_new`."
        class_new,class_old,file_path = change.new,change.old,change.owner.file_path
        fp = Path(file_path)
        parent = fp.parents[1]
        self._csv_dict[fp] = class_new