l10n WiP

This is a work in progress branch for adding localisation to Zippy.

Step one is to make Zippy play nice with Restify.

This branch has:

* Monkey patch to make nunjucks render available on the Response object (as would happen if we were using express)
* Monkey patch locals so that they work (needed for compatibility with i18n-abide).
* Add gettext and format calls around the the strings in the templates and use "set" so that swapping this out with real data later will be easier.