Jump to last read message is finished, 50%

UI / UX is working ok, next step is to reset the count & msgIDs on the
server side, then this will be ready for live deploy.
Unread message reset completed, unread msgs 100%

Unread messages are now collected, attributed to the right sender and
also enable the last read message to be shown with 1 click.

The unread messages are also reset when read, and in future could also
act as a 'message seen / unseen' counter, if desired.

This look ready to deploy.