Different font color for active and inactive groupbars

[rewgs]

For my groups, the active tab's groupbar has a light color, and inactives tabs' groupbars have a dark color. I'd love to be able to give the former a dark font, and the latter a light font. As it is now, though, both active and inactive tabs share the same font color setting.

[jirassimok]

This duplicates #7764, though that one is in the wrong category. (I'd assume this belongs in config feature requests.)