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
I added the `course_module` so I can use it to set the default license of any assets to the course license. If there is a way to just get the license from the course without loading the entire model, I agree that it should be changed to use that.