[M2] Integrate app2 with skywire-visor

[Darkren]

1. Rename app/network => app/appnet
2. Add appnet.RouterNetworker as described:
   So (appnet.RouterNetworker).Dial() functions will call (router.Router).DialRoutes(). The opts *DialOptions will be provided, internally by RouterNetworker
   In RouterNetworker, we need a Serve() function that calls Router.AcceptRoutes() in a loop.
   RouterNetworker will also need netutil.Porter: https://github.com/skycoin/dmsg/blob/mainnet-milestone2/netutil/porter.go

To assign ephemeral ports when dialing.
And reserve ports when Listening.
If we aren't listening on the local port specified in a receivedRouteGroup, close it immediately.
We also need to implement a net.Listener