R1:e5e5974d9fe1

Give typeahead browse dialogs sensible titles

Summary: Ref T4100. Let datasources specify a more meaningful title than the class name.

Test Plan: Browsed some sources.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: chad, epriestley

Maniphest Tasks: T4100

Differential Revision: https://secure.phabricator.com/D12469