Make Signal Service listen on a standard 443/80 port instead of 10000 (#396)

Right now Signal Service runs the Let'sEncrypt manager on port 80
and a gRPC server on port 10000. There are two separate listeners.
This PR combines these listeners into one with a cmux lib.
The gRPC server runs on either 443 with TLS or 80 without TLS.
Let's Encrypt manager always runs on port 80.

signal/client/grpc.go

@@ -75,6 +75,8 @@ func NewClient(ctx context.Context, addr string, key wgtypes.Key, tlsEnabled boo
 		return nil, err
 	}
 
+	log.Debugf("connected to Signal Service: %v", conn.Target())
+
 	return &GrpcClient{
 		realClient: proto.NewSignalExchangeClient(conn),
 		ctx:        ctx,