title: extjs treepanel expand collapse event
body: <p>I have a treepanel with nodes inside the treepanel. To identify whether the treepanel and not the nodes that are expanded or collapsed I use the following code: </p>
  
  <p>Ext.getCmp('general').collapsed</p>
  
  <p>The return value is either true or false. Is there an event in treepanel that I can capture when the treepanel is expanded or collapsed? I mean the treepanel and not the nodes in the panel. </p>
  
  <p>Your help is kindly appreciated.</p>
  
  <p>Thank You.</p>