Use the new "CurtainObjectRefList" UI element for subscribers
Also, improve the sorting and ordering behavior.
This makes the subscriber list take up a bit more space, but it should make it a lot easier to read at a glance.
Test Plan: Viewed object subscriber lists at varying limits and subscriber counts, saw sensible subscriber lists.
Maniphest Tasks: T13486
Differential Revision: https://secure.phabricator.com/D20967