Provide more information from diffusion.querycommits

Summary:
Ref T2783. Fixes T6039.

  - Provide `authorPHID` and `committerPHID` to resolve T6039.
  - In message parser, store author/email strings.
  - In cached results, emit author/email strings.

Test Plan: Called method with and without bypassCache. Used `reparse.php` to repopulate data on an old commit.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T2783, T6039

Differential Revision: https://secure.phabricator.com/D10424