Atc restructure folder code (Should not affect gh-book; depends on PRs)

should not affect gh-book but depends on #92 and probably #53

Folders used to be based on `container.coffee`. These changes make them more like `book.coffee`

# Testing

- [x] create a Chapter
- [x] move existing content into chapter
- [x] create new content
- [x] create a copy of content by dropping to a different book