title: sencha touch: Tab with no icon
body: <p>Is it possible to create a item in a tabbar-ed card layout, that has no tab? </p>
  
  <p>I want to create a message overlay that stretches from screen top to the tab bar and doesn't cover the tab bar. When i do this by adding an item to the panel everything works fine except a blank icon is created on the tabbar. Is there a way to prevent this icon from being created?</p>