[User Can] Change the text style on a single variant

[jcoliz]

This is allowed within the public interface now, it's just a matter of implementing it in config.

Couple different ways it can be done.

1. Set specific styles on each varying variant
2. Add arbitrarily-named style to the definition, then reference it in the variant.

Side note, also could vary text style by language, which is probably what we really want.