Add index page for coappearances and refactor routes.

- The route /coappear will show a list of chapters linked to each per-chapter visualization.
- Use Twitter Bootstrap (which uses jQuery in turn, so added that too) and Angular to build and style the content pages.
- Got rid of /static folder and split things into /data for JSON files, /assets for CSS and JavaScript, and /lib for third party static files of any type.