Display committed date in Revision Status field

Summary:
This is slightly more complicated for this reason:

• We don't set dateCommitted for normal commits, only for markcommitted.
  • We need to add this date to old revisions now.

Test Plan:
Reparse a revision - commit date was set.
Conduit markcommitted - commit date was set.
Run SQL script.
Display closed revision.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Koolvin

Differential Revision: https://secure.phabricator.com/D2282