Add a standalone view for browsing changesets of very large revisions

Summary: Ref T13110. Installs have various reasons for sending unreviewable changes (changes where the text of the change will never be reviewed by a human) through Differential anyway. Prepare for accommodating this more gracefully by building a standalone changeset list page which paginates the changesets.

Test Plan: Clicked the new "Changeset List" button on a revision, was taken to a separate page.

Maniphest Tasks: T13110

Differential Revision: https://secure.phabricator.com/D19295