Add support for private apps and remove support for vhost style port 80/443 bind
- Apps can now set label "network" "private" which will result in the frontend being bound to the private interface only
- Remove support for vhost style port 80 and 443 bindings - it's a nice idea but one could argue that it's out of scope for haproxy-marathon and a better alternative would be to run a haproxy or equivalent load balancer as a marathon app if that functionality is needed - it also frees up port 80 and 443 for other uses