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
First of all, you can just do `if (licenseable)` rather than `if (licensable === true)`. Second, it's weird that this table can have a different number of columns depending on the configuration. Can you make the License column *always* present in the HTML, and then use a CSS class to make it invisible if licensing is disabled? That way, there's no confusion or ambiguity around indexing. (When I edit the nth column in a row, I want to know what data I'm editing.)