* Controller_UserEnvironment is an abstract class, which defines $twig variable, and calls $twig->render in the after() method.
* $twig contains $twig->User variable by default.
* As I have read, it's totally recommended not to use $twig->Variables, so I defined $twig->set([params]) syntax
* Twig supports "fluent interface", so use $twig->set(...)->set_filename();
* Divided DeanOffice/Credits.php & moved part to Handler/

2. Рефакторинг

2. Загрузка списка студентов теперь работает корректно