new module purchase_delivery_address

The new delivery address in the purchase order is propagated to
the picking.
mto dropshipping: propagate address so->po
travis: split purchase_delivery_address
adapt to the existing dest_address_id field
update description
propagate the supplier as well

See the updated README for more infomation about the new logic. The idea
is to have in the picking information about both the supplier and the
customer address.
The test test_propagate_supplier_and_chosen_address_to_picking show also
clarify what is going on.
search picking types on the same company
Merge pull request #46 from lepistone/purchase_delivery_address

purchase_delivery_address