Make 'oudbesturen' an automatic mailinglist

Ghost User
2018-12-12T22:33:06+01:00

### Desired behaviour

Since all `boardxxyy@thalia.nu` mailinglists are automatically generated (https://gitlab.science.ru.nl/thalia/concrexit/commit/00d99502b2eb58d70ca30dd800432112a67b5ea5) we also want `oudbesturen`/`oldboard` to be automatically generated as well to prevent more work.