extension UIImage { class func loadAsyncFromURL(urlString: String, callback: (UIImage?) -> ()) { dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), { let url = NSURL(string: urlString) var err: NSError? let imageData = NSData(contentsOfURL: url!, options: NSDataReadingOptions.DataReadingMappedIfSafe, error: &err) var image: UIImage? if let _data = imageData { image = UII

