[FIX] account: re-introduce get_formview_id for invoices
[FIX] account: re-introduce get_formview_id for invoices

`get_formview_id` returns a view id to open
the document with. This method is meant to be
overridden in addons that want to give
specific view ids for example.

A link to an invoice must open a different form view
according if this is a customer or a vendor invoice.

This is handled by overriding `get_formview_id`
and returning the view id that should be used
according to something in the record
(e.g. according to the `type` field).

It was present in 8.0, it was somehow
removed in Odoo 9.0 during the refactoring
of the accounting modules, probably
for a wrong reason.

opw-673246

dfang/odoo,hip-odoo/odoo,laslabs/odoo,laslabs/odoo,Elico-Corp/odoo_OCB,bplancher/odoo,sysadminmatmoz/OCB,microcom/odoo,sysadminmatmoz/OCB,ygol/odoo,bplancher/odoo,hip-odoo/odoo,ygol/odoo,hip-odoo/odoo,sysadminmatmoz/OCB,Elico-Corp/odoo_OCB,dfang/odoo,bplancher/odoo,hip-odoo/odoo,ygol/odoo,Elico-Corp/odoo_OCB,ygol/odoo,microcom/odoo,sysadminmatmoz/OCB,storm-computers/odoo,bplancher/odoo,Elico-Corp/odoo_OCB,bplancher/odoo,bplancher/odoo,storm-computers/odoo,Elico-Corp/odoo_OCB,microcom/odoo,ygol/odoo,sysadminmatmoz/OCB,dfang/odoo,storm-computers/odoo,dfang/odoo,storm-computers/odoo,laslabs/odoo,ygol/odoo,laslabs/odoo,storm-computers/odoo,hip-odoo/odoo,laslabs/odoo,storm-computers/odoo,ygol/odoo,sysadminmatmoz/OCB,microcom/odoo,laslabs/odoo,dfang/odoo,sysadminmatmoz/OCB,microcom/odoo,microcom/odoo,dfang/odoo,hip-odoo/odoo,Elico-Corp/odoo_OCB