Traefik 2 Support

[johanhenriksson]

• Adds a new Traefik2Router that can create Ingress Routes for Traefik 2.
• Router type is now configurable using the router cluster option.
• Routers may store additional configuration in the cluster options.

Configuration example:

clusters:
  kubernetes:
    domain: cluster.yourcompany.com
    router: traefik2
    traefik2:
       entrypoints:
         - web
       middlewares:
         - https-only

resolve #36