title: Setting the frame for the preview layer results in incorrect frame settings
body: <p>I'm having some trouble with PBJVision.</p>
  
  <p>I integrated it into a Swift project and when I'm trying to set the frame of the preview layer, it results in an inconsistent frame:
  <img src="https://cloud.githubusercontent.com/assets/768893/12699384/e9824efc-c7c1-11e5-93b0-bb771ea450a8.PNG" alt="img_1678"></p>
  
  <p>I have this code:</p>
  
  <pre><code>var _previewLayer: AVCaptureVideoPreviewLayer = PBJVision.sharedInstance().previewLayer
  @IBOutlet weak var previewView: UIView! // this is the white view in the back
  
  let bounds = self.previewView.layer.bounds
  _previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill
  _previewLayer.bounds = bounds
  _previewLayer.position = CGPointMake(CGRectGetMidX(bounds), CGRectGetMidY(bounds))
  previewView.layer.addSublayer(_previewLayer)
  </code></pre>