#20 ban users

[Steffen Voß]

I know, you can't prevent anybody permanently from
posting, but it would be cool to have an easy function
to ban annoying users. One click and a function puts
the user into a group that isn't allowed to do anything
in the forum.

If the group (eg "pnForumBanned) doesn't exist yet, it
could be created and inserted as the first in the
permissions-list.