add / update list disarm / arm, which is only for sub-lists

add / update list disarm / arm, which is only for sub-lists

when a list is disarmed, its events aren't run.  Events can still
be added to it.  But because its event has been removed from the
parent timer, no events will ever run.

when a list is re-armed, it runs all events which have been
pending during the disarm period.  The caller is likely to clean
up events before re-arming the list