Add autoscroll to update log

[deadmeu]

The "View update log" element should autoscroll as new lines are added.

1. In the Software updates section, when updates are available, select "Install all updates"
2. Expand the "View update log" element
3. As the log entries fill the div, a scrollbar is created, but you have to manually scroll down as entries are added. It would be nicer if this could autoscroll automatically. Ensure that if you manually scroll up, autoscroll should be disabled, but if you manually scroll back down to the bottom of the list, autoscroll should be re-enabled.