make book use shared toc-node code
make gh-book pointer extend the common pointer code
Merge branch 'master' into atc-make-book-use-shared-toc-node

Conflicts:
	scripts/gh-book/toc-pointer-node.coffee
	scripts/models/content/book.coffee
Merge pull request #92 from oerpub/atc-make-book-use-shared-toc-node

Atc make book use shared toc node (Should not affect gh-book assuming other PRs merge)