Added the exhibition mode, if the flag is set in the configuration file, then you put any credentials in the login page and the Guest user logs in, it's a fully functional normal user. If the user is not part of any classes you run the script HACKADEMIC_INSTALL/misc_scripts/add_Guest_to_every_class.php to add the Guest to every class

Signed-off-by: Spyros Gasteratos <morfeas3000@gmail.com>