DocumentCleaner is missing clean_body_classes

[jeffnappi]

Add clean_body_classes from the python-goose upstream. Without this, there are cases where the body tag may get removed.

[codelucas]

Will do in 3 days! Thanks for bringing this up. (finals week in school right now)

[codelucas]

Ok this change is updated (version 0.0.7 for newspaper will be out soon with bug fixes, a big refactor, and more features)