Show a texture preview in addition to the framebuffer preview

It's cool to see what it's using to draw.

It's also interesting to see how we double up textures when bufw < w.  I wonder if we do crazy things when bufw > w, which is not impossible.  Maybe decoding could be faster if we just skipped the rest of the stride, not sure...

Of course, there will be garbage at the bottom of many textures (unless they align to a power of 2 in height), but there's no way to know the correct height so that's life.

Also includes some code shuffling in preparation to make the softgpu return a texture also (which it does not yet), and a fix for savestates not loading properly anymore.

-[Unknown]