Fixed pixel alignment in the Canvas widget

Xwt.WPF/Xwt.WPFBackend/DrawingContext.cs

@@ -39,6 +39,7 @@ namespace Xwt.WPFBackend
 				throw new ArgumentNullException ("graphics");
 
 			graphics.SmoothingMode = SmoothingMode.AntiAlias;
+			graphics.PixelOffsetMode = PixelOffsetMode.Half;
 			Graphics = graphics;
 		}
 

Xwt.WPF/Xwt.WPFBackend/WindowBackend.cs

@@ -48,6 +48,7 @@ namespace Xwt.WPFBackend
 		public WindowBackend ()
 		{
 			Window = new System.Windows.Window ();
+			Window.UseLayoutRounding = true;
 			rootPanel = CreateMainGrid ();
 
 			Window.Content = rootPanel;