The command resets the topic to the default as configured in uhub.conf.
"clear" wrongly implies that the topic will be emptied.
Also added a plugin description in plugins.conf.
Load plugin mod_topic, and it will provide 3 new user commands:
!topic - set new topic
!cleartopic - reset the topic (use default hub description)
!showtopic - show the current topic
Boris Pek
Jan Vidar Krey
Tillmann Karras