Improve browsability of Diffusion repository datasource

Summary: Ref T5750. Make browsing work and improve filtering.

Test Plan:

• Used browse UI.
• Used normal search UI.

{F373752}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5750

Differential Revision: https://secure.phabricator.com/D12434