title: Alignment of Android Expandable list view group indicator
body: <p>I want to change Exapandable listview group indicator. So I have tried like below:</p>
  
  <pre><code>&lt;ExpandableListView 
  android:layout_width="match_parent" android:layout_height="wrap_content"
  android:cacheColorHint="#00000000"      
  android:layout_marginTop="5dp"
  android:groupIndicator="@drawable/expandablelist_selector"/&gt;
  </code></pre>
  
  <p>expandablelist_selector.xml</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;selector xmlns:android="http://schemas.android.com/apk/res/android"&gt;
  &lt;item 
  android:drawable="@drawable/minus"
  android:state_expanded="true" &gt;&lt;/item&gt;
  &lt;item android:drawable="@drawable/plus"&gt;&lt;/item&gt;
  &lt;/selector&gt;
  </code></pre>
  
  <p>I have used 9 patch images. But the indicator is coming in top not in center. Please help me how to center group indicator icon/image.</p>
  
  <p>[Edit]</p>
  
  <p>Below is the dummy image reference:</p>
  
  <p><a href="http://tinypic.com/view.php?pic=o5oxkx&amp;s=5#.UqAcb9IW13N" rel="nofollow">http://tinypic.com/view.php?pic=o5oxkx&amp;s=5#.UqAcb9IW13N</a></p>