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
Looks like `course_info['license'].small_img` is supposed to return a HTML string. That's a really bad idea: it should just contain data, which is rendered to HTML using the templates. That's what templates are for.