Render commit summaries when rendering handles

Summary:
Fixes T2563. Instead of rendering "rPnnnnnn", render "rPnnnnnn: add feature X". Tweak Audit tables to accommodate.

@vrana / @nh, this migration might take a while. You could safely skip it when deploying and then run it after deployment.

I think I fixed all the other places where these render, but might have missed something.

Test Plan:
  - Ran first schema migration, clicked around to make sure nothing broke.
  - Ran `scripts/repository/reparse.php --message rXyyyyy`, verified summary populated.
  - Ran second migration.
  - Checked task/diffusion/audit/differential for weird rendering.

Reviewers: vrana

Reviewed By: vrana

CC: nh, aran, chrisbolt, allixsenos

Maniphest Tasks: T2563

Differential Revision: https://secure.phabricator.com/D5012