R1:a438c87c52f7

Show the difference between a committer and an author

Summary:
Git and hg (supposedly..) differentiate between an author (who wrote the patch)
and a committer (who applied the patch).

This patch allows Phabricator to note when a patch is committed
by someone other than the Author.

Test Plan:
Created 2 accounts,
- U (Account with a PHID)
- U' (Account without a PHID)
and had them create and commit commits

testing if their username/real name would be displayed correctly in Diffusion,
- BrowserTable…