Fix: create User Acount without session (#665).

When a User Account topic is created (via dms.createTopic()) while no session exists (that is no user is logged in) no exception occurs. The created User Account topic (and its child topics) will have no creator/owner/ACL information. It's up to the developer to set these manually afterwards.

See #405.
See #665.
Merge branch 'master' into workspace-acl