One transfer move for each payment.order

New implementation of transfer moves: 1 transfer move for each payment.order (and not each payment.line) with only 1 line in the transfer account for the total of the account move.

Other small changes:
- Move the inherit of the 'Invoice' button of payment.order from account_banking_payment_transfer to account_banking_payment_export
- Demo data: Add a bank account + mandate on Agrolait, to be able to easily test multi-partner SEPA DD