Versions our nginx config as of right now

This versions the app-specific part of our nginx config.

For the SSL configuration see [`ssl.rules`](https://github.com/18F/DevOps/blob/262c2114020de61148f84cab649c818bfd214e6c/nginx/ssl/ssl.rules) in our DevOps repo. (Soon to be moved into [ssl-standards](https://github.com/18f/ssl-standards).)