Adds ChessPiece's species hardsuit sprites

Adds @ChessPiece's onmob and inventory sprites for unathi and skrell hardsuits, as well as nicer tajaran hardsuit inventory sprites to replace the current placeholder ones. Adds hardsuit spritesheet entries for unathi.

I've added the skrell hardsuit sprites to the *.dmi files but I'm holding off on the sprite sheet entries for now. Since humans and skrell can wear the same hardsuits and humans can wear skrell helmets, the sprite sheets will cause the same suit to look different on mobs depending on species. This isn't a big deal, but I thought I should ask here or perhaps open a forum thread first.