add new module purchase_transport_document

This module adds a new object transport.document and allows to choose
those in the purchase order.
add security, doc, demo data
demo -> data

Those examples of transport documents are fairly common, so I always
include them (not only as demo data).
fix typo in manifest
make name translatable, add i18n template
lading is a word!
Add delivery_remark/remark+pass it to rfq/rfq line
move doc to README.rst
Merge pull request #37 from yvaucher/8.0-purchase_requisition_bid_selection-add-delivery_remark

Add delivery_remark/remark+pass it to rfq/rfq line
Merge pull request #35 from lepistone/purchase_transport_document

add new module purchase_transport_document
add purchase_requisition_transport_document

this depends on https://github.com/OCA/purchase-workflow/pull/35
propagate transport documents from tender to rfq
test that zero and one documents are propagated
test that two documents are propagated