FactTree: don't reset y position in set_facts()
Created by: mwilck
set_facts() is called every minute to update the time of the current activitiy. If the y position is reset to 0 in set_facts(), this causes the fact list to be scrolled to the top once a minute, irritating users.
Fix it by simply not resetting the y position. This Resolves #594 (closed).