Added key bindings to sort the change list by number (current default), and by
the time the change was last updated. Also added the ability to reverse the
sort, useful for showing the most recent changes at the top of the screen.
Doesn't depend on but sorting by updated column makes more sense with this
patchset: https://review.openstack.org/#/c/122176/
Change-Id: I4d0ee462c106e26857785c9b4e26cc17e906796a