Tidy up transport delete items

Make the url generation work proerly (though I'm fairly sure we don't
actually need the url as an argument to delete) and remove
debug print statement *blush*

Make bulk_delete use delete() instead of bulk delete from REST

ItemTransport clas --> transport.items module

Replace with ItemTransport object, which needs to be instantiated. I
think it can be reused between calls to its methods so there's no need
to create new ones all over the place, but that's what I have done so
far. I'm a bit uncertain about module level variables, and not
everything is contained in a class.

Actualy they are now also a class.
The existing functions still exist and call into the class
(wastefully creating an instance every time but I expect these
to go away and rewrite the clients to use an instance of the
transport class directly.