Mostly drive Calendar event recurrence with the RRULE engine

Summary:
Ref T10737. Today, we evalute recurrence twice: once when querying, and once in all other cases. This converts the second case to use the RRULE engine.

Next up is making the query use the RRULE engine, too.

Test Plan: Created a new recurring event, iterated through it by clicking "next instance", viewed it on Calendar view.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10737

Differential Revision: https://secure.phabricator.com/D16667