Allow to do a dropshipping with a subcontractor.
If the product uses the routes drophipping and have
a subcontracting BoM. Then a PO for the subcontractors
will genrate a need in the subcontracting location for
the required components.
A module is needed because the picking_type_id for dropshipping
do not have a warehouse_id. The warehouse_id is needed in order to
know from which warehouse the subcontracting components should be
deliver.
