Backend tests

All serialisers and views currently have 100% coverage. Closes #50 (closed). As every bit of code needs tests a general test issue is not required. Code that wants to be merged into master should be completely tested anyway.

backend/core/tests/test_student_page.py

+from rest_framework.test import APIClient, APITestCase
+from util.factories import GradyUserFactory
+
+
+class StudentPageTests(APITestCase):
+    @classmethod
+    def setUpTestData(cls):
+        cls.factory = GradyUserFactory()
+        cls.student = cls.factory.make_student(username='student01', matrikel_no='12345',
+                                               exam='Exam01')
+        cls.tutor = cls.factory.make_tutor(username='tutor01')
+        cls.reviewer = cls.factory.make_reviewer(username='reviewer01')
+
+