Migrate Gruntfile to CoffeeScript

Change-Id: Id900a6a303df04430763e90e4d36d6726c99549d
Move css to external stylesheet

Change-Id: If9dc26504cb7bb100a4680f8b4d49477405a10e6
Use idiomatic coffee script in Gruntfile

Change-Id: I7bedf669adb77512ef1f4f066a43c9ad1fe08b52