Render build status on revisions and commits

Summary:
This uses an event listener to render the status of builds on their buildables.  The revision and commit view now renders out the status of each of the builds.

Currently the revision controller has the results for the latest diff rendered out.  We might want to show the status of previous diffs in the future, but for now I think the latest diff should do fine.

There's also a number of bug fixes in this diff, including a particularly nasty one where builds would have a build plan PHID generated for them, which resulted in handle lookups always returning invalid objects.

Test Plan: Ran builds against diffs and commits, saw them appear on the revision and commit view controllers.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T1049

Differential Revision: https://secure.phabricator.com/D7544