Prevent item deletion on enter key

If the user is editing an existing item and presses enter, AngularJS
will do an onClick() on the first submit button, which is the (usually) hidden
delete confirmation button in this case. We only want to confirm delete
if the user has previously clicked on the X previously, though.
Display message when packed list is empty

Show a short message to the user explaining how to move items into the
packed list, if there are items and none of them have been packed.