Messages arriving while a conversation was open were never marked as read,
so the chat list kept showing them as unread after going back. The screen
now marks incoming messages read while it is on top and the app is in the
foreground, again when the app returns to the foreground, and on leaving.
Read state is now monotonic in Conversation.updateMessage, so a stale copy
of a message (attachment download, delayed resend) can no longer flip it
back to unread.
Also create the swipe-to-reply animation controller lazily instead of in
dispose().
Julius Joska