title: put icon at left of each button in spark ButtonBar flex 4
body: <p>hello all i have the following:</p>
  
  <pre><code>&lt;s:ButtonBar id="tabs" y="15" left="0" height="31"
               change="VideosMenuBar_changeHandler(event)" requireSelection="true"&gt;  
      &lt;s:layout&gt;
          &lt;s:HorizontalLayout gap="1" columnWidth="180" variableColumnWidth="false"   
                              /&gt;
      &lt;/s:layout&gt;
  
      &lt;s:ArrayCollection&gt;
          &lt;fx:String&gt;Latest Videos&lt;/fx:String&gt;
          &lt;fx:String&gt;Last Week Videos&lt;/fx:String&gt;
          &lt;fx:String&gt;Last Month Videos&lt;/fx:String&gt;
      &lt;/s:ArrayCollection&gt;
  
  &lt;/s:ButtonBar&gt;
  </code></pre>
  
  <p>can anyone tell me how can i embed an icon to the left of each button of this (spark)ButtonBar?? I have searched all the web!</p>
  
  <p>Thanks beforehand!</p>