base: make BankAccount.getReference use BankAccount.getIban
When IBAN is defined, use it by default for reference. IBAN is used by default all over europe, so when it's set it should be used by default for reference. Mixing IBAN and other properties does not make sense, so this change should not have unexpected side effects.
We also update "edit_order" on BankAccount_view so that title properly fallbacks on reference when reference is iban.