Improve bank accounts selection on accounting transactions
Fix small problems displaying bank accounts on accounting transactions and be more strict during validation:
- bank account must be validated
- bank account must belong to the section
The latter was a problem for scenarios like this:
- create transaction for supplier 1 with supplier 1 bank account
- clone transaction
- change to supplier 2 the bank account remains as supplier 1 bank account, although it became an invoice from supplier 2. The transaction could be validated as long as the bank account is not invalidated