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
What is `license_img`, and why is it an HTML string? Again, templates are used to turn data into HTML. Pass data to the template, not HTML.