R1:65329204a5f2

T5464, ApplicationTransactions for calendar events

Summary: Closes T5464, Implement ApplicationTransactions in Calendar.

Test Plan: Create a calendar event, update calendar event, detail view of event should show update history.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: johnny-bit, Korvin, epriestley

Maniphest Tasks: T5464

Differential Revision: https://secure.phabricator.com/D12586