Simplify the TYPE_INVITE Calendar Event transaction for EditEngine

Summary:
Ref T9275. Now that TYPE_ACCEPT and TYPE_DECLINE have been separated out, we can simplify TYPE_INVITE.

This now just takes a list of invited PHIDs, uninvites ones that were removed and invites ones that were added. This is simpler, lets more logic live in the Editor, and makes EditEngine/API access easier.

Test Plan: Created events, added and removed invitees. Used comment stacked action and "pro" editor to adjust invitees.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9275

Differential Revision: https://secure.phabricator.com/D16280