Update dependencies; Minify css on production

There’s actually a few changes in here:

  * Add README instruction for compiling sass
  * Remove typecsset dependency (and therefore bower dependency). typecsset was called in master.scss, but never actually used – in fact, none of the bower stuff is (it’s all loaded from google CDN and the like). Is that deliberate, @jonic? Should we just drop bower?
  * Add css minification to the heroku build script.