Added resize masks to the loading view for the AVCaptureScannerView

When the device is landscape, and the scanning starts, a loading view shows, but it wasn't stretching correctly in landscape.  This fixes the autoresizemask so it stretches properly.  Fixes #100

src/ZXing.Net.Mobile/iOS/AVCaptureScannerViewController.cs

@@ -47,8 +47,13 @@ public void Cancel()
 
 		public override void ViewDidLoad ()
 		{
-			loadingBg = new UIView (this.View.Frame) { BackgroundColor = UIColor.Black };
-			loadingView = new UIActivityIndicatorView (UIActivityIndicatorViewStyle.WhiteLarge);
+            loadingBg = new UIView (this.View.Frame) { 
+                BackgroundColor = UIColor.Black, 
+                AutoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleHeight 
+            };
+            loadingView = new UIActivityIndicatorView (UIActivityIndicatorViewStyle.WhiteLarge) {
+                AutoresizingMask = UIViewAutoresizing.FlexibleMargins
+            };
 			loadingView.Frame = new RectangleF ((this.View.Frame.Width - loadingView.Frame.Width) / 2, 
 				(this.View.Frame.Height - loadingView.Frame.Height) / 2,
 				loadingView.Frame.Width,