Add tests for AssignmentController
Additionally, this commit adds tests for each existing controller test to check whether the defined endpoints are authorization-checked (for regression purposes mostly).
Also, this commit adds a JacksonTest class to test whether the running configuration for LabraCORE registers the date time modules for Jackson in such a way that LocalDateTime objects can be serialized and deserialized.
Finally, this commit of course tests a number of things in AssignmentController. Mainly AssignmentController's methods are tested for creating the right database objects.
Closes #27 (closed)