Added some helper methods

Xwt/Xwt.Drawing/Context.cs

@@ -232,6 +232,11 @@ namespace Xwt.Drawing
 			handler.Translate (Backend, tx, ty);
 		}
 		
+		public void Translate (Point p)
+		{
+			handler.Translate (Backend, p.X, p.Y);
+		}
+		
 		public void Dispose ()
 		{
 			handler.Dispose (Backend);

Xwt/Xwt/Point.cs

@@ -67,10 +67,12 @@ namespace Xwt {
 			return X.GetHashCode () ^ Y.GetHashCode ();
 		}
 		
-		public void Offset (double dx, double dy)
+		public Point Offset (double dx, double dy)
 		{
-			X += dx;
-			Y += dy;
+			Point p = this;
+			p.X += dx;
+			p.Y += dy;
+			return p;
 		}
 		
 		public bool IsEmpty {

Xwt/Xwt/Rectangle.cs

@@ -177,6 +177,12 @@ namespace Xwt
 			}
 		}
 		
+		public Point Center {
+			get {
+				return new Point (X + Width / 2, Y + Height / 2);
+			}
+		}
+		
 		// Inflate and Offset
 		public Rectangle Inflate (Size sz)
 		{