DRAFT Add db columns for recurring events

Summary: Ref T2896, DRAFT Add db columns for recurring events

Test Plan: Open event, confirm it still works.

Reviewers: chad, Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: btrahan, Korvin, epriestley

Maniphest Tasks: T2896

Differential Revision: https://secure.phabricator.com/D13039