change from throwing a Http404 exception, which I believe will try to render a static 404.html template - and ironically triggers a 500 server error. Just create a HttpResponse and set the status_code to 404.

refactor StaticContent id scheme to be the same as moduledata. Also expose a new 'get all content for course' which will be needed to support a asset management page.

per feedback, use reverse() when generating callback urls. Also generate thumbnails when ingesting static images. We'll need these handy for the CMS UI.

Support asset library references in CapaModule. Also some code refactoring/cleanup. Preparing for review and submit