Merge remote-tracking branch 'processone/pr/2763'

* processone/pr/2763:
  disallow room creation if archive not empty and clear_archive_on_room_destroy is false
  check if mod_mam is loaded before calling mod_mam:is_empty_for_room
  added cmds to list and destroy empty rooms by ejabberdctl
  allow check if archive is empty for or user or room
  option to prevent archive removal on room destroy