title: How to use NativeBase DatePicker
body: <p>Given this <a href="https://github.com/GeekyAnts/NativeBase/blob/v2.5.1/src/basic/DatePicker.js" rel="noreferrer">DatePicker Api</a> from NativeBase v2.5.1 how am I supposed to capture the change date event with the new selected date?</p>
  
  <p>If I understand well the selected date is only available in the internal state of the component:</p>
  
  <pre><code>setDate(date) {
      this.setState({ chosenDate: new Date(date) });
  }
  </code></pre>
  
  <p>I imagine I can use the react native ref api but it doesn't seem right since other similar components do offer the onDateChange event, eg: <a href="https://github.com/xgfe/react-native-datepicker" rel="noreferrer">react-native-datepicker</a></p>