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'm disinclined to sort by a non-indexed field, can we just remove the sort here since the order doesn't matter for the zip format?