File Box - ability to move files #76

Once we have the select working, we need to add the ability to move/cut/paste files w/in a file box.

Ideally, that would involve adding drag-and-drop support so that when a file is dragged to a folder, it gets moved there.

Also add support for cut and paste which just store the file IDs and file box UUIDs on the client side. On paste, make the API calls to move those resources to the current context.