Admin panel folding

@liuhenry @mattlebel 

sections in the admin panel now fold/collapse when clicked so that a user can reduce clutter/scroll faster/find things more easily.

everything other than a couple of minor css changes implemented via coffeescript, so users without javascript enabled will still see the same layouts. for future reference, add `default_expanded` class to prevent `foldable` class divs from collapsing on page load.