title: adding another CALayer atop of a AVCaptureVideoPreviewLayer
body: <p>I'm trying to add another later atop of a AVCaptureVideoPreviewLayer. I have tried adding it above the preview layer, in the viewdidload and a few other things. still no joy. Anyone have any ideas?</p>
  
  <pre><code> func configureCaptureSession() {
      captureSession.sessionPreset = AVCaptureSession.Preset.photo
  
      let deviceDiscoverySession = 
  AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInDualCamera], 
  mediaType: AVMediaType.video, position: .unspecified)
  
      for device in deviceDiscoverySession.devices {
          if device.position == .back {
              rearCam = device
          } else if device.position == .front {
              frontCam = device
          }
      }
  currentDevice = rearCam
      guard let captureDeviceInput = try? AVCaptureDeviceInput(device: 
  currentDevice) else {
          return
      }
      wheelOverlay.image = UIImage(named: "wheel")
      wheelOverlayLayer.contents = wheelOverlay
      stillPhotoOutput = AVCapturePhotoOutput()
  
      captureSession.addInput(captureDeviceInput)
  
      captureSession.addOutput(stillPhotoOutput)
      view.layer.addSublayer(wheelOverlayLayer)
  
      cameraPreviewLayer = AVCaptureVideoPreviewLayer(session: 
  captureSession)
      view.layer.insertSublayer(cameraPreviewLayer!, below: 
  wheelOverlayLayer)
      cameraPreviewLayer?.videoGravity = 
  AVLayerVideoGravity.resizeAspectFill
      cameraPreviewLayer?.frame = view.layer.frame
      print("Capture session setup")
     // view.layer.addSublayer(wheelOverlayLayer)
     // view.layer.insertSublayer(wheelOverlayLayer, above: 
  cameraPreviewLayer)
      captureSession.startRunning()
  
  
  }
  </code></pre>