Legalpad - denormalize a field or two from DocumentBody to Document

Summary: this let's the list controller save a query. Fixes T3488. Note didn't bother denormalizing document body at all since I don't think we want to show a snippet.

Test Plan: viewed a list of legalpad documents - yay. viewed a legalpad document - yay. created a legalpad document - yay. edited a legalpad document - yay. edited with N authors - yay.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T3488

Differential Revision: https://secure.phabricator.com/D6382