chore(build): Adding Sass to Grunt pipeline

Adding Sass and Autoprefixer into the mix. This also means we need a dist/ directory, so things are about to get "weird".

Took a rough stab at documenting the available Grunt tasks, although some are subject to change once we get minification and other things involved.
This is borderline hacky and offensive since it just copies all the raw code from one pile to another. Once we get usemin+rev wired in, we'll want to probably redo this so the scripts/** gets minimized after being copied.