This PR introduces some backend python + REST APIs for storing static asset files along with an XBlock in a content library. It also updates the new runtime to be able to load such static asset files. Example use cases: * Store an image file with an HTML block and then use the image inline in the HTML block. * Store a PDF file with an HTML block and provide a link in the HTML for the learner to download the PDF. * Store .srt files or even video .mp4 files that belong to a video XBlock. Within the bundle, these static asset files are stored in a "static/" subfolder of the folder that contains the OLX file. Extending an existing LMS/Studio convention, a static asset file such as "image.png" is referenced within the OLX as "/static/image.png" and the URL will be rewritten by the runtime.
XBlock App Suite Tests ====================== Where are they? As much of the runtime and XBlock API code depends on a learning context, the XBlock and XBlock Runtime APIs (both python and REST) in this django app are tested via tests found in `content_libraries/tests <../../content_libraries/tests>`_.