Fixes:

- Include TaEnrollment as a valid enrollment type when getting class and section lists from SDK
- Reverse order of sending enrollment_type and enrollment_role to SDK method and make them named parameters instead of positional
- Enforce that section_id and enrollment_id are post parameters that must be present by allowing KeyError to trigger if either is not in the POST
- Add tests to check for above conditions, as well as one that ensures the SDK enroll method is called with expected parameters