Move non-comment transactions to a separate history view in Ponder

Summary: Ref T3373. Most edits aren't too interesting, put them on a separate history page.

Test Plan: Viewed question page; viewed history page for question and answer.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3373

Differential Revision: https://secure.phabricator.com/D6612