Events on expand/collapse

Added events to trigger on expand and on collapse.
Then events are triggered for the list as well for each list item. The client choose which to listen to.

```javascript
$('#nestedlist').on('expand', function(e, li){
    var id=li.data('id');
});

$('#nestedlist').on('expand', '[data-id=5]', function(e){
    var id=$(this).data('id'); //id=5
});
```