Improve messaging of special policy rules in applications

Summary: Ref T603. When the user encounters an action which is controlled by a special policy rule in the application, make it easier for applications to show the user what policy controls the action and what the setting is. I took this about halfway before and left a TODO, but turn it into something more useful.

Test Plan: See screenshots.

Reviewers: btrahan, chad

Reviewed By: chad

CC: chad, aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D7265