Scroll to unread marker when selecting chat

[nesium]

The unread marker is super helpful for catching up with a lot of messages. If the number of unread messages doesn't fit on one page however, I'd rather start at the first (oldest) unread message and work my way down to the most recent one, so that I can read them in chronological order.

This is of course more complicated than it seems, right to the point where one asks when we finally get our own MAM implementation with the features that we need. But for a first implementation it might suffice to scroll up to the first unread message if it is contained in the batch returned by loadUnreadMessages (unless that's already the case?).