Added OnMouseWheel missing properties in bgravirtualscreen

bgravirtualscreen.pas

@@ -107,6 +107,9 @@ type
     property OnMouseLeave;
     property OnMouseMove;
     property OnMouseUp;
+    property OnMouseWheel;
+    property OnMouseWheelDown;
+    property OnMouseWheelUp;
     property OnResize;
     property OnStartDock;
     property OnStartDrag;