#30 Remove nick option

[Bryan Ex]

It would be nice to allow the option to registered players
to delete their nick from the WebChess database or
perhaps just exclude it from the inviteplayers.php page
so it doesn't cause errors elsewhere (like if they had
played a game already for example). I've had a few
people now that have registered just to take a look only
to ask me to delete their registration after being
challenged to a game. To do this now means manually
editing the database each time. Maybe an option on
mainmenu.php to "Allow challenges" setting a 0 or 1
assigned to their nick with only 1's being listed in the
drop down list of players?