show hide item

[jonasosterberg]

It would be a nice feature to be able to show or hide a single menu item.
Maybee setVisible(item, visible) similar to the setDisabled

Example implementation:
`
setVisible: function (item, visible) {
var container = this._container;

if (!isNaN(item)) {
	item = container.children[item];
}

item.style.display = visible ? '' : 'none';

},
`