Convert all the graphics to png.

Pic compression is now lossless thanks to stag doing all the work. This lets all graphics be png. These are converted to 2bpp/1bpp/pic during the build. Building both Red and Blue from scratch takes about 25 seconds (compared to 12 or so before). Subsequent builds aren't affected.

While GitHub has decided this isn't mergeable, I had no trouble merging locally.