Publish QoS -1/Out of session considerations

Whatever we call publish QoS -1/out of session, we should call them by the same name as they are the same thing, just used for different versions of the protocol 1.2 and 2.0.

The 1.2 version should be clearly marked as for backward compatibility.

I do think the new version ought to have a protocol version field as in the connect packet - just one byte. We have gained two bytes by omitting the packet id field, so I think this is fine. It feels odd to not have it.