Add support for * in window classes

Hey, I don't think I'm able to explain clearly so I'll give an example.

I don't want rounded corners on any of my steam games, and rather than have a bunch of _steam_app_548516_ blackisted (one for each of my games), I think it'd be cool to be able to just have one _steam_app_*_ which would blacklist all apps starting with _steam_app_ from rounded corners.

Thanks.