Make Harbormaster build plan datasource more browsable

Summary: Ref T5750.

Test Plan:

• Browsed plans in Harbormaster.
• Browsed plans in typeahead browser.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5750

Differential Revision: https://secure.phabricator.com/D12435