Add shipments reference on invoice

Following discuss: https://discuss.tryton.org/t/add-shipment-reference-on-invoice/340

assigned to @maxx

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New review360721002 at https://codereview.tryton.org/360721002/#ps376471002

review360721002 updated at https://codereview.tryton.org/360721002/#ps387731002

review360721002 updated at https://codereview.tryton.org/360721002/#ps397101003

review360721002 updated at https://codereview.tryton.org/360721002/#ps397331002

review360721002 updated at https://codereview.tryton.org/360721002/#ps384461002

review360721002 updated at https://codereview.tryton.org/360721002/#ps393741002

New changeset a8ffeea52d87 by Maxime Richez in branch 'default':
Add shipments reference on invoice
https://hg.tryton.org/modules/account_invoice_stock/rev/a8ffeea52d87

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closed

New changeset c273d7cd6e6d by Cédric Krier in branch 'default':
Add shipments reference on invoice
https://hg.tryton.org/tryton-env/rev/c273d7cd6e6d

mentioned in issue #11148