JELP needs dynamic mode negotiation

[cooper]

Currently mode definitions are only sent during burst. There is also no mode to remove modes once they're registered. Need to make AUM/ACM commands more dynamic with module loading and stuff. Also need a way to tell servers when modes are no longer available.

    It is now necessary for servers to track which of its own modes are familiar to
    other servers. This way, a server can determine if it needs to send out ADDUMODE,
    ADDCMODE, AUM, or ACM commands when new modes are added.

    Example: a new module was downloaded from the repository. The server configuration
    updated to include the mode provided by the new module. The server is rehashed.

    The server has tracked its own modes and is aware that NO servers are aware of the
    new mode, so it sends an ACM message to all servers. Mode-adding commands should
    be forwarded only if they occur outside of a burst.

[cooper]

See #63.