Add do_thickinthehead to run thickinthehead when --all is set.
Rewrite relabel_surface() to accommodate more cases, and to include erase_remaining option.

erase_remaining : set all values not in old_labels to erase_value
Update mindboggle to accommodate new relabel_surface()
Use DKT31 labels vs. DKT25 labels in tables.

Revise write_shape_stats() so that cerebrum_cortex_numbers are used instead of cerebrum_cortex_numbers_DKT25.  Comment out DKT25 definitions in LABELS.py.