added a value for gridkey_rows "auto". In this setting, if delta2 is off, gridkey_rows is filled by unique items found in all_plot_groups. if delta2 is on, gridkey_rows is filled by concatenating "x1_level" and "experiment_label".
The order of the gridkey_rows items are by the order of appearance in the xlabels. If delta2 is on, then the items are ordered in groups by experiment and x
Added parser for gridkey_rows