Rename PhabricatorSettingsPanel subclasses for consistency
Summary: Ref T5655.
Test Plan: arc lint and arc unit
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T5655
Differential Revision: https://secure.phabricator.com/D11136