Bug/import

Publish was breaking if the were children references to non-existent items. Because import uses publish, this was breaking imports of some courses.

Import was breaking if a tar.gz had a directory in it w/ the same name as the root dir which occurred importing some MITx courses with manifest files.

@ormsbee @cpennington plz review
This is moving everything from `dirpath` inside of `course_dir`. I don't see why having a directory inside `dirpath` named the same as `course_dir` would be a problem (unless the file in question is actually a symlink to `..`, which I've seen in some MITx courses).