Notify supervisor of supervisee yearly revalidation - Quick link to revoke supervision

When a supervisee revalidates his account during a yearly revalidation process, the supervisor should be notifed in order to quickly check if the revalidation claim is based on proper supervision information.

The supervisor can drop the email notification if all is correct or should be able to quickly revoke this supervision claim if needed through a temporary link given in the email.

Related to #542 (closed)