Copy and customization of nginx.conf

- Copied (https://github.com/aws/opsworks-cookbooks/blob/release-chef-11.4/nginx/templates/default/nginx.conf.erb) from aws opsworks-cookbook.
- Adding connection processing method with optimized `epoll` default.
- Adding support for `worker_rlimit_nofile`.
- Adding application/json to default gzip_types.

should there be a default for log_dir? it seems weird to have error.log be put at the root level by default.