#38 Guests can choose a nickname

[DarthCode]

When someone writes a post without being logged in, his
posting will appear under a standard name like "guest"
or "anonymous" in pnForum. That makes it very difficult
to differentiate between several guest users. In many
other forums there is a possibility to choose a
nickname before submitting a post as guest user, e.g.
in the "pforum"-software
(http://test.powie.de/pforum/). Certainly there should
also be a function that protects the nicknames of
registered users against being chosen by guest users.