Restrict Differential buckets to just ApplicationSearch views

Summary: Ref T9363, If we're in a dashboard panel, only show buckets with data, or a fallback if nothing exists.

Test Plan: Test 'active revisions' panel in a dashboard and in Differential.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T9363

Differential Revision: https://secure.phabricator.com/D17544