Make Panels slightly easier to find and use

Summary: Ref T10390, turns "add existing panel" into a typeahead, and add lots more information to search.

Test Plan: Add an existing panel, click the search icon, see more information (type, engine).

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T10390

Differential Revision: https://secure.phabricator.com/D17348