Calendar event timeline feed should reflect invite changes better
Summary: Ref T7988, Calendar event timeline feed should better reflect invite changes.
Test Plan: Create or edit calendar event, invite or remove users, save, timeline feed should correctly reflect added/removed invitees.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: Korvin, epriestley
Maniphest Tasks: T7988
Differential Revision: https://secure.phabricator.com/D12625