Calendar events should be green if viewer is invited, and grey if not.

Summary: Closes T8189, Calendar events should be green if viewer is invited, and grey if not.

Test Plan: Check that month and day views display events that viewer is invited to as green and grey otherwise, including month day badges on mobile monthly view.

Reviewers: chad, Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T8189

Differential Revision: https://secure.phabricator.com/D12850