Summary: Closes T7940, Calendar events should have edit/view policies.
Test Plan: Create new event and save, event should be only visible and editable by creator. Editing policies should correctly set the permissions of editing/viewing the event.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: Korvin, epriestley
Maniphest Tasks: T7940
Differential Revision: https://secure.phabricator.com/D12632
