Add Faenza-based themes by nemesis5

Unexpected jackpot when browsing gnome-look.org. These are really good,
GPLed, and from known GPLed source (Faenza). Yay.

http://gnome-look.org/content/show.php/gnect-theme?content=149669
Remove Cream Marbles theme and change the default

Let's use a default theme based on the Faenza icon for Four-in-a-Row.
Do not name the themes Faenza without permission

Haven't heard back from the Faenza themes author yet. We shouldn't use
the name Faenza in our application unless we're sure it's OK for us to
do so.
Update artwork credits
Add additional COPYING file for new themes
Merge branch 'faenza-themes'