Add email preferences to Pholio

Summary: Fixes T5386, adds a base set of email preferences to Pholio

Test Plan: Turned on, tested and got email, turned off, tested and saw notifications.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5386

Differential Revision: https://secure.phabricator.com/D9644