Plumb link labels through to layout

LayoutLink.js

@@ -1,7 +1,8 @@
 class LayoutLink {
-  constructor(from, to, nodesByPos, linksByPos) {
+  constructor(from, to, label, nodesByPos, linksByPos) {
     this.from_ = from;
     this.to_ = to;
+    this.label_ = label;
     this.nodesByPos_ = nodesByPos;
     this.linksByPos_ = linksByPos;
     this.bfs();
@@ -178,6 +179,9 @@ class LayoutLink {
     return (this.getOutPoint(from, to) + 4) % 8;
   }
 
+  drawLabel() {
+  }
+
   getSteps() {
     let steps = [];