CORS for Dokku

[almereyda]

Currently this data service is served via Dokku, which uses nginx to terminate HTTP connections. This is also the CORS proxy, while eventual headers have to be set there.

The reason nginx is the best way is that nginx is the fastest and closest process to the client.
http://serverfault.com/questions/670219/nginx-proxying-nodejs-dokku-cors-response-headers-not-passing-through

Few resources come up that lead a path towards implementation for us:

• CORS support? What's the simplest way? dokku/dokku#997 (comment)
• https://gist.github.com/MichaelJCole/2d6d30c6d4e19495c425