Adam/generalized draft import export 2

@dmitchell -- is this the right idea?

https://openedx.atlassian.net/browse/TNL-574
It seems odd to have this check on DIRECT_ONLY_CATEGORIES. Why not just look for parent_url or parent_sequential_url? I assume it would never happen that something is in DIRECT_ONLY_CATEGORIES AND has parent_url or parent_sequential_url.