Discussion nginx

The beginning of moving discussion over to our own stack so we can eat some cookies.
[See here for example](http://comments.theguardian.com/discussion/p/3tycg).

This is an attempt to move rendering to the right place i.e. The Play app.

This does mean that people are going to have to start running their stack through nginx if they want to see comments whilst developing, or using the direct URL.