Added "selected" binding to kendoPanelBar

Why: There should be a selected binding to go along with the expanded binding on kendoPanelItem so that you can do something like this:

<ul data-bind="kendoPanelBar: {}">
   <li data-bind="kendoPanelItem: { expanded: IsExpanded, selected: IsSelected}">
      Panel 1 Content
   </li>
   <li>
      Panel 2 Content
   </li>
</ul>

What: Added a selected binding

How: The selected binding calls the select method to select the proper panel