title: Extjs Panel - Set click a button on tbar
body: <p>I define a <b>'panel'</b> extend: 'Ext.form.Panel' that has a tbar with three buttons. 
  <br>when my other work done i want my 3nd button on tbar must click to do some task. 
  <br>I don't want create a new function with same task like panel.myfunction().
  <br>Any way to do that thanks</p>