Thanks for making this! Some suggestions:
1. You should register "selectCol" as non sortable, on init, because it 1)doesn't actually sort 2)confuses the Group By Sort view;
2. It would complete the functionality if you could add an onclick listener to the column header and then toggle between Select All and Clear Selection (maybe with a tristate icon - none, some, all selected).
3. A tooltip on the column header would be good.
4. The optional large font is good, but please add an option for the regular sizing, ie a css rule that sets the icon at 16x16, the max for all other stock icons.
Thanks for the excellent suggestions. I've added them in 1.2.