Introduce display of relational structures (experimental)

Change-Id: I3f8f16ff477e0ff21d846a4a0799a8e48f3f43e4
diff --git a/dev/js/src/match/tree.js b/dev/js/src/match/tree.js
index dc4f229..88f0542 100644
--- a/dev/js/src/match/tree.js
+++ b/dev/js/src/match/tree.js
@@ -162,8 +162,15 @@
       return this;
     },
 
+    // Dummy method to be compatible with relTree
+    show : function () {
+      return;
+    },
+
     /**
      * Center the viewport of the canvas
+     * TODO:
+     *   This is identical to relations
      */
     center : function () {
       if (this._element === undefined)