Less file in root dir.
Simplify QuestionIO::getQuestions().
Fix broken test cases.
Remove QuestionIO::getQuestions().
Remove quiz_get_question_types(), a duplication of quiz_question_get_info().
Rename quiz_question_get_info() to quiz_question_get_plugin_info().
Rename hook_quiz_question_info_alter to hook_quiz_question_plugin_info_alter.
Revert last change.