WIP#203 Adding autoprefixer to clean up some of the scss files.

I've removed as many browser prefixed css attributes as I thought would be a good idea. I left `normalize.scss` because I don't want to screw things up. I noticed that the protip 3d animation when you preview your protip was broken when I removed all of the prefixed attributes in `protip.scss` so I left some of those that were making that happen.