Ability to invite users, but no RSVP capability yet.
Summary: Ref T7986, Ability to invite users, but not RSVP yet.
Test Plan: Open event, add invitees, save, event detail view should show invitees.
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T7986
Differential Revision: https://secure.phabricator.com/D12617