Display local commit information in Differential

Summary:
After D857, we try to attach local commit information to revisions. If this
information is available, display it on the revision.

Design on this is a little rough, I might try to combine this into the revision
update view or something like that since we're starting to take up a lot of real
estate for metadata.

Test Plan: Local diffed this and got some commit info.

Reviewers: jungejason, tuomaspelkonen, aran

Reviewed By: jungejason

CC: aran, epriestley, jungejason

Differential Revision: 872