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'm torn about your decision to pass `imgSize` directly to `LicenseSelector`, rather than including it in the model. On the one hand, the model should have all the data necessary to render the view. On the other hand, `imgSize` seems like a piece of information that is specific to how the model is rendered, not specific to the information in the model.

For now, I'd rather you move as much information as possible into a model, and then we can pull stuff out later in the code review if it seems awkward to have it stuffed into the model.