Diviner: improve links, book index, and atom view

Summary: Ref T988. Minor improvements to diviner: link stuff to a valid endpoint which actually works; fix group names on the book index; improve the topics index for atom views.

Test Plan: Clicked links in an article, viewed book index, viewed an article with long headers.

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T988

Differential Revision: https://secure.phabricator.com/D6598