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 that try...except block really necessary? Could you catch just a specific Exception type (like in ``except KeyError:``), at least? Otherwise you may more easily run into problems with an unexpected exception being caught.