Are we on screen to load image?
var imageURL: NSURL? {
    didSet{
      image = nil
      if view.window != nil { //Are we on screen?
          fetchImage()
      }
      
    }
  }var imageURL: NSURL? {
    didSet{
      image = nil
      if view.window != nil { //Are we on screen?
          fetchImage()
      }
      
    }
  }