Complete rewrite of WikiUser.php.

Complete rewrite of WikiUser.php.

This should make it easier to hook in user permission groups etc. some
time in the future. Most importantly, to finally get UserPreferences
fully working properly for all classes of users: AnonUser, BogoUser,
AdminUser; whether they have a NamesakePage (PersonalHomePage) or not,
want a cookie or not, and to bring back optional AutoLogin with the
UserName stored in a cookie--something that was lost after PhpWiki had
dropped the default http auth login method.

Added WikiUser classes which will (almost) work together with existing
UserPreferences class. Other parts of PhpWiki need to be updated yet
before this code can be hooked up.

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@2884 96ab9672-09ca-45d6-a79d-3d69d39ca109