Add contact and invoice party

Following https://discuss.tryton.org/t/add-contact-and-invoice-party-on-orders/1813

assigned to @ced

added purchasing sales type::feature + 1 deleted label

Here is review274701003

added 1 deleted label and removed 1 deleted label

review274701003 updated at https://codereview.tryton.org/274701003/#ps274721002

review274701003 updated at https://codereview.tryton.org/274701003/#ps288981003

I'm wonering if we should use also the same desing on project_invoice module. So you have the party (and contact) for which the project is done and the party where you have to invoice it.

Project are much long running document. Usually we have to customize it to add very specific roles linked to the company workflow. I do not think we solve any real use case with the same design from sale.

review274701003 updated at https://codereview.tryton.org/274701003/#ps286721002

review274701003 updated at https://codereview.tryton.org/274701003/#ps268971003

review274701003 updated at https://codereview.tryton.org/274701003/#ps266901002

review274701003 updated at https://codereview.tryton.org/274701003/#ps295131003

New changeset 3dcf447df526 by Cédric Krier in branch 'default':
Add contact and invoice party
https://hg.tryton.org/modules/party/rev/3dcf447df526

added 1 deleted label and removed 1 deleted label

closed

New changeset 69f659bdf3b3 by Cédric Krier in branch 'default':
Add contact and invoice party
https://hg.tryton.org/modules/purchase/rev/69f659bdf3b3

New changeset bcabcde731a9 by Cédric Krier in branch 'default':
Add contact and invoice party
https://hg.tryton.org/modules/sale/rev/bcabcde731a9

New changeset 5d5cbd1c7ff9 by Cédric Krier in branch 'default':
Add contact and invoice party
https://hg.tryton.org/modules/sale_credit_limit/rev/5d5cbd1c7ff9

New changeset 20fb10829667 by Cédric Krier in branch 'default':
Add contact and invoice party
https://hg.tryton.org/modules/sale_invoice_grouping/rev/20fb10829667

New changeset 0edab7b3010a by Cédric Krier in branch 'default':
Add contact and invoice party
https://hg.tryton.org/modules/sale_opportunity/rev/0edab7b3010a