title: Ext JS - get value of toggleGroup when default type is button
body: <p>How to get value of toggleGroup when default type is button. 
  allowblank:false is also not working.</p>
  
  <pre><code> {
          xtype:'radiogroup',
          fieldLabel: 'What is your title?',
          layout:'hbox',
          allowBlank:false,
          defaultType: 'button',      
          id: 'titleSel',
          defaults: {
              enableToggle: true,
              toggleGroup: 'titleGroup',
              allowDepress: false,
              width: '16.56%',
              name: 'title',
          },                      
          items: [
              {text: 'Mr', value: 'Mr', inputValue: 'sfsf'},
              {text: 'Mrs', value: 'Mrs'},
              {text: 'Madam', value: 'Madam'},
              {text: 'Ms', value: 'Ms'},
              {text: 'Dr', value: 'Dr'},
              {text: 'Prof', value: 'Prof'},          
              ],
          },
  </code></pre>