Registration of custom chat commands and menu-items for protocols was
done by the IM_REGISTER_* messages, and is now done through direct calls
to the CayaProtocol object.
The new model for call/message for protocols is this: Temporary
information (chat messages, roster members, etc.) should be accessed
through messages. Relatively static data (protocol name, commands)
should be accessed through direct calls to the protocol object.
Use IM_MESSAGEs, IM_REGISTER_COMMAND and IM_REGISTER_USER_ITEM, for
registering commands and user-list pop-up items.
The former replaces CayaProtocol::Commands(), which was a real bad idea
in the first place. Just awful. No idea why I did that instead of this,
which is nicer and significantly easier anyway.