Add a "Recent Builds" element to the Build Plan UI and tighten up a few odds and ends

Summary:
Depends on D20218. Ref T13258. It's somewhat cumbersome to get from build plans to related builds but this is a reasonable thing to want to do, so make it a little easier.

Also clean up / standardize / hint a few things a little better.

Test Plan: {F6244116}

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13258

Differential Revision: https://secure.phabricator.com/D20219