in derivatives of Ox.List, make sure gainFocus, hasFocus and loseFocus work correctly

source/Ox.UI/js/List/Ox.TreeList.js

@@ -259,6 +259,20 @@ Ox.TreeList = function(options, self) {
         }
     };
 
+    that.gainFocus = function() {
+        self.$list.gainFocus();
+        return that;
+    };
+
+    that.hasFocus = function() {
+        return self.$list.hasFocus();
+    };
+
+    that.loseFocus = function() {
+        self.$list.loseFocus();
+        return that;
+    };
+
     return that;
 
 };