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.
https://github.com/henrikjoreteg/fixpack is pretty rad.
Also https://github.com/gorillamania/package.json-validator (http://package-json-validator.com/) can be very useful.