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.