Add Node.js reflector client disconnect notification

This fix sends an event to all clients letting them know when a client has disconnected.  There is some additional logic in the Ruby server 'onDisconnect' which may be applicable to the Node reflector.

To test:

Open the browser debug console, <ctrl> <shift> j
Execute the test/clientNotification test (e.g. http://localhost:3000/test/clientNotification/)  
Note the logged msg in the browser console, "vwf.view.document: Client Joined:  http-vwf-example-com-clients-vwf:....."
Open up another browser/tab pointing to the same application instance.
Note the 2nd "Client Joined" msg in the browser console
Now close the 2nd (latest) application instance (browser/tab window)
Note the logged msg in the browser console, "vwf.view.document: Client Left:  http-vwf-example-com-clients-vwf:..."

This last message indicates that a disconnect notification was distributed & received properly.