Add a 'policy' command

Original LP Author: Barry Warsaw , LP Link: https://bugs.launchpad.net/bugs/1070064

It would be kind of nice for MM3 to implement a 'policy' command. If you issue this email command, you would receive a response containing an admin supplied policy text. This response should adhere to the general grace period timeouts, and the text should be retrieved via the generalized url retrieval and caching machinery. This way, the same policy text could be retrievable via email command or web ui.

There should be a way to request policy documents in multiple languages.