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 commented out for now, but makes it easy to have Sass minify the content if we wanted. Or maybe not. Sass gets run first, then autoprefixer on the generated CSS, so maybe the minification and sourcemaps need to happen later in the pipe.