#4 add moderation to Guestbook

[Marius Scurtescu]

Please implement an optional moderation for the
Guestbook. This will allow all signatures to be
reviewed before they go live.

You could base moderation on groups. For example
Anonymous users are moderated and Registered users are
not. Even more, you can disable signing for Anonymous,
moderate Registered and don't even moderate some
special group.

Thanks