Creative Commons Licensing for edX

This PR adds Creative Commons Licensing to the Open edX Platform.

Review tickets
T&L https://openedx.atlassian.net/browse/TNL-195
UX https://openedx.atlassian.net/browse/UX-948
Please do not load the whole course if you don't actually need it. To simply check if a course exists, use

```python
if not modulestore().has_course(course_key):
    logging.error("Could not find course: %s", course_key)
    return HttpResponseBadRequest()
```