Migration for purchase payment

Adds payment info to the purchase process.

Adds payment type, terms, and bank account to the purchase orders.

Allows to set different default payment terms for purchases (the partners will have payment terms and supplier payment terms).

The payment terms, payment type and bank account default values for the purchase will be taken from the partner.

Invoices created from purchase orders, or from pickings related to purchase orders, will inherit this payment info from the payment order.