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
At the moment, you are allowed to pass either an object having the respective attributes (which is the usual procedure due to SQL-Alchemy) or a dictionary having the respective entries (which might be easier when using json). At the moment, this is quite useless, but I thought of adding some "slider bar" to the details page, so that you could lower limits without having to reevaluate the test.