Remove dead code
Test that a model exists before trying to retrieve its page
Add support to get a page by id as well as page number
Performance improvements

Avoid using Backbone.Associations' event handling due to performance penalties,
and reduce unnecessary page redraws.
Don't try to load a page if no page exists to load
Match a page to an id with or without a version number
Prerender HTML for performance and fix contextual links
Cleanup code spacing
Move scroll and analytics methods into media view
Fix missing page/book toggle
Merge pull request #616 from Connexions/collection-context-links

Performance Improvements & Collection context links