Adding the NODE MENU button

We have created a node menu scene that displays examples of the nodes in a game. We are now going to add a button on the main menu, which will allow users to access the node menu scene:

1. Firstly, we have to create an instance of NodeMenuScene in the beginning with the following line of code:

   var nodeMenuSceneInstance : NodeMenuScene?

2. Now, we have to set attributes of the NODE MENU button label, as we did for the Level: label earlier. For this, add the following code in the addNodeMenuSceneBtn() method and call it from the didMoveToView() method also:

   func addNodeMenuSceneBtn()
      {
          var backbutton = SKLabelNode(fontNamed: "Chalkduster")
          backbutton.fontColor = UIColor.cyanColor()
          backbutton.name = "NODEMENU"
          backbutton.text = "NODE MENU"
          backbutton.position = CGPointMake(CGRectGetMaxX(self.frame) - backbutton.frame.width/2 , CGRectGetMaxY(self.frame) - backbutton.frame.width/8)
          backbutton.zPosition = 3
          self.addChild(backbutton...