Users that are VLAB Group Managers cannot be deleted

When trying to delete a user account that is a VLAB group manager, the following exception is thrown:

Caused by: org.postgresql.util.PSQLException: ERROR: update or delete on table "users" violates foreign key constraint "fkkcd7k1w0xyty9ogqfrnk7em82" on table "domain_group_managers"
  Detail: Key (id)=(8) is still referenced from table "domain_group_managers".

It would be best if a warning message is shown with a list of all domain groups where the given user is a manager, and an option for the admin to choose whether the user should be deleted nevertheless (thus removing the group manager role)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information