lncli: Add graphical output of routing table

LIGHT-131, LIGHT-140, LIGHT-138
`lncli showroutingtable` may output routing table as image.
Use graphviz for graph rendering.
Add explicit version dependency for tools. Add error checking.

rpcserver.go

@@ -512,15 +512,15 @@ func (r *rpcServer) ShowRoutingTable(ctx context.Context,
 	in *lnrpc.ShowRoutingTableRequest) (*lnrpc.ShowRoutingTableResponse, error) {
 	rpcsLog.Debugf("[ShowRoutingTable]")
 	rtCopy := r.server.routingMgr.GetRTCopy()
-	channels := make([]*lnrpc.RTChannel, 0)
+	channels := make([]*lnrpc.RoutingTableLink, 0)
 	for _, channel := range rtCopy.AllChannels() {
 		channels = append(channels,
-			&lnrpc.RTChannel{
-				Id1:      channel.Id1.String(),
-				Id2:      channel.Id2.String(),
-				EdgeID:   channel.EdgeID.String(),
-				Capacity: channel.Info.Capacity(),
-				Weight:   channel.Info.Weight(),
+			&lnrpc.RoutingTableLink{
+				Id1:       channel.Id1.String(),
+				Id2:       channel.Id2.String(),
+				Outpoint:  channel.EdgeID.String(),
+				Capacity:  channel.Info.Capacity(),
+				Weight:    channel.Info.Weight(),
 			},
 		)
 	}