Copy wl_notificationtimestamp when copying watchlist entries on move

When a page is moved, the new title is automatically added to the
watchlists of every user watching the old title. But we also need to
copy the wl_notificationtimestamp over, otherwise edits from before the
move aren't highlighted in the page history and such.

Bug: 73219
Change-Id: I657475c28944539daec14f838d3af4c2962a4b93