Reading/Multimedia/Architecture

This is a stub article that will eventually be a description of our multimedia architecture.

Technical debt

 * API upload is all kind of bad. everything under the directory /upload would be nice to rewrite.
 * backlink invalidation in commons would be nice to fix
 * versioned urls for thumbnails
 * large file support in general - deadlocks abound
 * way FileRepo stores files is bad in general...requires pessimistic in general
 * Why chunked upload should be fixed:
 * Upload actions that go through the job queue should be more reliable.