Prevent creation of automatic mailinglists

Ghost Userrequested to merge
fix/mailinglist-creation into master

Closes #703 (closed)

Previous behaviour

Steps to reproduce:

  1. Create mailinglist that is also an automatic list
  2. Created

New behaviour

Steps to validate that it works:

  1. Create mailinglist that is also an automatic list
  2. Creation blocked

Merge request reports