Menu: Add default null callbacks and update unit tests

Author: kborchers

tests/unit/menu/menu_defaults.js

@@ -8,6 +8,9 @@ commonWidgetTests( "menu", {
 		},
 
 		// callbacks
-		create: null
+		blur: null,
+		create: null,
+		focus: null,
+		select: null
 	}
 });

ui/jquery.ui.menu.js

@@ -24,7 +24,12 @@ $.widget( "ui.menu", {
 		position: {
 			my: "left top",
 			at: "right top"
-		}
+		},
+
+		// callbacks
+		blur: null,
+		focus: null,
+		select: null
 	},
 	_create: function() {
 		this.activeMenu = this.element;