Make Differential load lint/unit data from Harbormaster

Summary: Fixes T8095. Still needs UI/UX work (see T8096) but this has all the core features now.

Test Plan: Saw Harbormaster lint/unit data as though it was Differential lint-unit data.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8095

Differential Revision: https://secure.phabricator.com/D13401