[MotionGraphs] Fix UIView ctor to be called from nib

initWithCoder: ctor is the one called when loading a view from a Xib/Nib while
we actually implemented this ctor in GraphView we never actually exported it
so unmanaged land can call our managed version of it.

MotionGraphs/MotionGraphs/GraphView.cs

@@ -58,6 +58,7 @@ public GraphView (CGRect frame) : base (frame)
 			CommonInit ();
 		}
 
+		[Export ("initWithCoder:")]
 		public GraphView (NSCoder coder) : base (coder)
 		{
 			CommonInit ();