Update downloader functionality to split out media files (video + audio) to be sideloaded as dependencies

[rtibbles]

Description

There are significant challenges with nesting video and audio files in zip files - mostly that it is not possible to universally support Range requests from inside zipfiles (c.f. learningequality/kolibri#7776 (comment))

With le-utils v0.1.28 and above, we have available both video and audio dependency format presets - this means that we can unpack and side load any media files during HTML5 zip generation. Adding this to our downloader functionality will also allow us to standardize proper paths for referencing external files in a way that uses relative paths and is not vulnerable to different deployment scenarios.