Immediately display outgoing MUC message, update on reflection

When doing XMPP over a high-latency link (or to a very slow MUC service), sending a message makes it disappear, and it might or might not come into view later. It would be much better to mimic the behavior known from private chats, where the message is displayed immediately, and updated when the MUC reflects it (also considering that the body might be rewritten by mod_trashbin).

It would be great to have the green checkmark as an indicator of successful reflection.

Thanks.