[TextKitDemo] Fix ctor, we must use initWithCoder when loading from a…

… storyboard

initWithCoder: is the designated initializer for views built from the storyboard
since we are not creating the Cell programatically by calling
RegisterClassForCell we must export initWithCoder: ctor to unmanaged world so
when it needs to create a new cell it calls into our managed initWithCoder:
and do the initialization we want.

TextKitDemo/TextKitDemo/CollectionViewCell.cs

@@ -9,6 +9,17 @@ namespace TextKitDemo
 	public partial class CollectionViewCell : UICollectionViewCell
 	{
 		public CollectionViewCell (IntPtr handle) : base (handle)
+		{
+			Initialize ();
+		}
+
+		[Export ("initWithCoder:")]
+		public CollectionViewCell (NSCoder coder) : base (coder)
+		{
+			Initialize ();
+		}
+
+		void Initialize ()
 		{
 			BackgroundColor = UIColor.DarkGray;
 			Layer.CornerRadius = 5;