[IMP] account: add 'partial' and 'reversed' payment states to invoices

- 'partial' payment state corresponds to invoices whose payable/receivable move line has been partially reconciled with some other line.

- 'reversed' payment state corresponds to entries that have been cancelled by the creation of a single reverse entry (using the dedicated button on the form view). This state can be set on invoice as well as on regular entries.

=> To stay consistent with the naming conventions, this commit also renames invoice_payment_state field to payment_state, since it's no longer only applicable on invoices.

closes odoo/odoo#41723

Related: odoo/enterprise#7202
Signed-off-by: Quentin De Paoli (qdp) <qdp@openerp.com>