Add costumes for the overworld sprites

This is still a WIP but thought I'd make a pull request so you can check it out.

There's a problem with overlapping tiles - if you go from forest -> forest 2 -> town the bodies go underneath the blue trees but the arms stick out the side. I assume this is because we increased the sprite size to 36x36 (but didn't change the arm length).

Still need to
* add Shirley's overworld sprites (Ben355 is working on this)
* add Pillowman Pierce (image done, just not added)
* check the guys costumes
* change Kevin's base costume to the naked one on reddit