Feedback and Unit Tests

* Feedback: table columns shown on "submissions" page depend on feedback
* Unit Tests:
    * changed semantics
    * implemented server-sided unit tests
    * seperate unit tests from normal submissions
    * special "details" page
Is it because the constructor of ScoreType (the super-constructor) calls max_scores which itself calls is_unit_test? Does that make sense before set_submission_info gets called?