Slightly improve Buildable list in Harbormaster

Summary:
Ref T10457. This makes diffs/revisions show the revision as the buildable title, and commits show the commit as the title.

Previously, the title was "Buildable X".

Also makes icons/colors/labels more consitent.

Test Plan:

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10457

Differential Revision: https://secure.phabricator.com/D15355