Re-implement calendar.invite transactions

Summary:
Fix T11339.
Now, old and new are both simple lists of phids, and the rendering should make sense.

Test Plan: Viewed existing transaction with all 3 states.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Maniphest Tasks: T11339

Differential Revision: https://secure.phabricator.com/D16311