Edit recurring ghost events, not recurring event.

Summary: Closes T8358, Edit recurring ghost events, not recurring event.

Test Plan: Create recurring event, original event should not be editable, but ghost events should be editable.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T8358

Differential Revision: https://secure.phabricator.com/D13075