Provide ANSI color information for Harbormaster build status via API

Summary:
Ref PHI261. This moves Harbormaster build status to work more similarly to other modern status types, like Differential revision status, where we try to specify as much behavior on the server as possible so that the client and server can vary independently.

(I don't have any specific plans to make Harbormaster build status configurable on the server side, but it isn't out of the question.)

Test Plan: Ran harbormaster.querybuilds (saw same data as before) and harbormaster.build.search (saw same data as before, plus new ANSI color data).

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Differential Revision: https://secure.phabricator.com/D18838