Add CCs -> Add Subscribers
Summary: I think this is the direction the language has been moving? Maybe this will train me that "CCs" are called "Subscribers". (I actually don't love this wording change, but consistency is good?)
Test Plan: {F163255}
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D9367