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
This seems like the wrong place to handle which editor to use. Can you integrate this into the existing logic, instead of adding your own at the end?