Bugfix: Class CommonCookie not found when moving the library folder

When moving the library folder to some other location and updating the parameters.yml to reflect this change you will get a fatal error on every request.
Fatal error: Class 'CommonCookie' not found in /data/project/xxxxxxxx/htdocs/frontend/core/engine/model.php on line 561

The autoload.php script did not use the PATH_LIBRARY constant, this has been fixed.