title: Sencha touch - change back button text for image in NavigationBar
body: <p>I'm usign Sencha Touch 2.1 so this code should work (<a href="http://www.sencha.com/forum/showthread.php?188982" rel="nofollow">link I used for inspiration</a>):</p>
  
  <pre><code>defaultBackButtonText: null,
          useTitleForBackButtonText: false,
          backButton: {
              // ui: 'toolbar-back',
              // align : 'left',
              iconCls: 'back',
              iconMask: true
          },
  </code></pre>
  
  <p>But I can still see icon and text as well.</p>
  
  <p>Thanks a lot.</p>