Skintone fixes.

1. Fetuses generated with a particular non-mixed race selected will always have skintones within that race's natural genetic range.  Mixed race fetuses remain unrestricted.
2. Catgirl fetuses will now get natural catgirl coloration instead of ordinary human skintones.
3. Catgirl natural skins are now in their own category so the `naturalSkins` guard on `skinToMelanin` works correctly.
4. Cheat mode will now offer natural skintones for catgirls from the catgirl list, and natural skintones from non-catgirls from the ordinary list.
5. The invalid "crinkled" hairstyle will no longer be set on some black slaves (instead, they'll have "afro").