Remove Proxy JID; Add Stable Participant ID; + Remove reommendation to generate Nick as UUID;
A user will typically set a nick when joining a channel and MAY update this nick from time to time. The user does this by sending a command to the channel to set the nick. This command is a <setnick/> child element of <iq/> element. The <setnick/> element is qualified by the 'urn:xmpp:mix:core:0' namespace. The nick is encoded as a <nick/> child element of the <setnick/> element. If the user wishes the channel to assign a nick (or knows that the channel will assign a nick) the nick field can be left blank, so that the user can see what is assigned in the result.