share permissions and common tests for all profile types, improve tests

oser_cs/tests/factory.py

oser_cs/tests/test_api/mixins.py

oser_cs/tests/test_api/model_api_boilerplate.py

oser_cs/tests/test_api/test_schoolstaffmember_api.py

oser_cs/tests/test_api/test_student_api.py

oser_cs/tests/test_api/test_tutor_api.py

oser_cs/tests/test_users/mixins.py

oser_cs/tests/test_users/test_profile.py

oser_cs/tests/test_users/test_school_staff_member.py

oser_cs/tests/test_users/test_student.py

oser_cs/tests/test_users/test_tutor.py

oser_cs/tests/test_utils.py

oser_cs/tests/utils/__init__.py

oser_cs/tests/utils/test_cases.py

oser_cs/tutoring/utils.py

oser_cs/users/models/profiles.py

oser_cs/users/views.py