Add clear chart button and improve chart menu look&feel

backend/src/Model/TreeNode.ts

@@ -52,10 +52,6 @@ export class TreeNode<ViewModel extends Destroyable> {
     return this.sourceEdge ? this.sourceEdge.source || undefined : undefined
   }
 
-  public hasMessage() {
-    return this.message && this.message.value && this.message.value.length !== 0
-  }
-
   private isTopicEmptyLeaf() {
     return !this.hasMessage() && this.isLeaf()
   }
@@ -108,6 +104,10 @@ export class TreeNode<ViewModel extends Destroyable> {
     }
   }
 
+  public hasMessage() {
+    return this.message && this.message.value && this.message.value.length !== 0
+  }
+
   public destroy() {
     this.onDestroy.dispatch(this)
     this.onDestroy.removeAllListeners()