Start the private pub server with Foreman

When developing locally, start both Unicorn and the private pub server with `foreman start`, rather than having to start each separately by hand.

I'm pretty sure this will have adverse effects when you deploy this app to Heroku (I'm not sure how you have private pub set up in production). If so, I can change this to be in a `Procfile.dev` that can be started with `foreman --procfile=Procfile.dev` instead. Let me know.