Adds 'setSubHead' to Objectlist

Summary: There are a few places a third text row in ObjectItemListView is needed or make things easier to read. Built and rolled out in Config.

Test Plan: Tested in Config Groups.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5837