Checked items now work

This address issue #118.  The download and delete actions work as expected.  Internally, there are two new endpoints: resource/download GET and resource DELETE.  The download can actually get item, folder, user, and collection resources, and the delete can work on any model that has a remove method.
I know we aren't consistent about this, but I personally would find this more readable as `window.encodeURIComponent`, since it's one of those symbols I don't see very often (unlike `console` or `JSON`).