Adam/generalized draft import export 2

@dmitchell -- is this the right idea?

https://openedx.atlassian.net/browse/TNL-574
if you're importing something which a user copied & modified from the published into the draft subdir, it may not have the 2 expected attrs. (user could also have removed the draft parent from the draft subdir but not the child and then the child would not have the attrs)