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.
Also, I'm just ignorantly copying over the _entire_ `bower_components/**` tree (~3MB currently). Not sure if we want to micro-optimize and only copy over the ~10 files that we need/use.

For example:
- backbone/backbone.js
- jquery/dist/jquery.min.js + jquery/dist/jquery.min.map
- etc.

Actually, that may not be the most sustainable of plans...