Public Course Import/Export API (WIP)

This is a public, shared, versioned, RESTful API for importing and exporting full course content. The code was initially ripped from the existing import/export API in the CMS contentstore djangoapp and wrapped in Django Rest Framework view classes.
This PR includes configuration changes. Most notably, Studio is configured to serve the OAuth2 provider alongside the LMS.

I'm marking this as WIP for now because there are 29 lines which are missing test coverage. Most of the offending lines are error conditions which are also missing coverage in the original import code, such as handling of multipart file upload errors.