Thalia Pay: Export payment batches for ING
Export payment batches for ING for #632.
Because we want Thalia Pay (#632).
Export option for payment batches in the right format. These batches can be used to execute a direct debit batch.
- Need to determine the format with the treasurer.
- We can do this by adding extra payment actions to the payments admin that only exports payments marked for direct-debit (#930 (closed)).
- The selection for which time the payments are exported can already be selected using Django's built-in date filter.
- The mandate 'last used' field should be updated upon export of the payments.