Replace PNG sprite with SVG sprite

This should be ready to go. I switched out the PNG sprite with SVG sprites, for resolution independence. Sadly, cursors don't suppor SVG so those still need to be PNG's.

I also ended up fixing #1246 while working in this branch, so that's part of this pull request too.

It'd be great if someone double checked this for me before merging. Works fine for me in Safari/Chrome/FF/Opera.