Rewritten StatisticsServiceTest, Statistics is testable on equality
Make use of spring security to secure service methods
Included ApplicationPermissionEvaluator in security config

Permission handling is the same as with removed Authorized annotation
Removed obsolete code

Spring security based permission check will do this for us.
Reworked permission evaluator for use with all types of authentication
Use pre/post authorization for QuestionService were possible
Added tests for LecturerQuestionControllerTest
Minor code cleanup