[Wpf] Add alert dialog options support

Xwt.WPF/Xwt.WPFBackend/AlertDialogBackend.cs

@@ -55,7 +55,7 @@ namespace Xwt.WPFBackend
 		public Command Run (WindowFrame transientFor, MessageDescription message)
 		{
 			this.icon = GetIcon (message.Icon);
-			if (ConvertButtons (message.Buttons, out buttons)) {
+			if (ConvertButtons (message.Buttons, out buttons) && message.Options.Count == 0) {
 				// Use a system message box
 				if (message.SecondaryText == null)
 					message.SecondaryText = String.Empty;
@@ -98,6 +98,12 @@ namespace Xwt.WPFBackend
 					};
 					box.PackStart (stext);
 				}
+				foreach (var option in message.Options) {
+					var check = new CheckBox (option.Text);
+					check.Active = option.Value;
+					box.PackStart(check);
+					check.Toggled += (sender, e) => message.SetOptionValue(option.Id, check.Active);
+				}
 				dlg.Buttons.Add (message.Buttons.ToArray ());
 				if (mainBox.Surface.GetPreferredSize (true).Width > 480) {
 					text.Wrap = WrapMode.Word;