Beautiful art, and more!

With the help of GeneralWadaling, we now have a whole pixel art style for the Undead! We also have a new unit, the Angel of Death, to replace the Nuclear Missile. It's a super-powered bomber unit, but beware, it costs money every time you use it! Plus a couple tweaks to game balance, with the hopes that when the AI plays the Undead, it will get off its ass and go conquering instead of saying home and building Wonders all day.