R1:dc389c90bb62

Simplify policy header implementation

Summary: Instead of rendering this in all callers, just pass the object into the header and let it figure out how to format it.

Test Plan: Looked at Legalpad, Paste, and Pholio.

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D7039