Policy - make policy transactions render better in email

Summary: right now you get sent an email with a broken link 'cuz the email is plain text if you edit something with the edit policy being a project.

Test Plan: edited a legalpad document edit policy repeatedly to various projects. observed good emails via bin/mail debug tool. object page still looked good too

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Differential Revision: https://secure.phabricator.com/D7149