Performance Improvements & Collection context links

Improve performance when navigating between pages in a book by removing Backbone.Associations from handling some events and processing HTML changes in the body before adding them to the DOM.

Also update all links in the body to other modules in the same book to point to simply load the page inside the book, rather than as a stand-alone page.

This PR also restores the Book/Page toggle to the History tab.

Fixes #588, Connexions/rhaptos.cnxmlutils#54