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
• HistoryTable
• Code revision

Teztz,
A(uthor)/C(ommitter)
If it's A/A then Author committed

UL = User link (<a href="/p/username">username</a>)
UN = User name ("Firstname Lastname")

Tezt | Expected in table | Got

A/A | UL/UL | UL/UL
A'/C | UN/UL | UN/UL
A/C' | UL/UN | UL/UN
A'/C' | UN/UN | UN/UN

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Koolvin

Maniphest Tasks: T688

Differential Revision: https://secure.phabricator.com/D2541