Button icon span

Working branch right now up for functional review for button re-write demo at http://view.jqueryui.com/button-icon-span/demos/button/

Spec: http://wiki.jqueryui.com/w/page/71756381/Button
Both uses of this flag invert the value. Let's change it accordingly:

```
this.noTitle = !this.title;
[...]
if ( this.noTitle ) {
```