Populate results of DiffusionQueryCommitsConduitAPIMethod with DiffusionLowLevelCommitQuery

Summary:
Ref T2783. This populates the following fields in DiffusionQueryCommitsConduitAPIMethod using DiffusionLowLevelCommitQuery when bypassCache is set to true:

• authorName
• authorEmail
• committerName
• committerEmail
• message
• hashes

The original outline called for authorPHID and committerPHID as well (but no message field). As far as I can tell, the PHIDs aren't actual a property on DiffusionCommitRef, and since the intention of this is to be able to populate a DiffusionCommitRef, I haven't included them. Let me know if we really do need the PHIDs here.

Test Plan: Tested using 3 Phabricator instances (one web, one taskmaster and one storage). The web and taskmaster tiers are directed at the Conduit API of the storage tier. Made a diffusion.querycommits from the Conduit app on the web tier instance and saw the data populated from the raw VCS data (located on the storage tier).

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T2783

Differential Revision: https://secure.phabricator.com/D10399