Documented the various overlay and animation change traits

They all kinda sound the same, are often named very generic and used hard-coded sequence names that forced people to read the source code or wait for the game to crash to find out. This should improve https://github.com/OpenRA/OpenRA/wiki/Traits a lot in that regard. Includes some minor cleanup as well.
Still then RA is like the only mod where WithResources is not used. I don't see the problem. https://github.com/OpenRA/OpenRA/pull/5321 will clean this up anyway.