Send read markers for read messages

Currently, if the last read message is actually visible on the screen, all messages currently on the screen are markes as read. this means that when scrolling down from there, the read marker follows the user and when the user opens the chat and sees the newest message, the backlog is not marked as read (if it's long enough).

Please test well.

What currently does not work is opening a chat and jumping to the last read message if that message is not loaded yet. if that happens, scroll up until that message is loaded