Display message errors in chat log

[ge0rg]

When delivery of a message fails, this is not visible to the user. However, it would be much better to have an indication that the message was not delivered.

This indication should NOT be displayed if a Receipt has been received for that message already, and it should be reset if a Receipt arrives after the fact.

This is how it looks in yaxim:

P.S: you can test the behavior by sending messages to xmpp:reject@yax.im