Show thread user to staff when only anonymous_to_peers is true

FOR-122
This does not work. Read the documentation for the map function.

Also, `has_access` checks the main course permissions, but we use a separate permission framework for the forums. The function you should use is `cached_has_permission`. There's no specific permission for this case, but I think it would be fine to use another permission that is reserved for moderators like `"openclose_thread"`.