Close modal and update display field with custom button

Right button in Navigator has a very low visibility so I was thinking of adding a custom button in Modal view to close the modal and select the value. So far I'm able to close the modal but not able to update the display value of the field. Any suggestion?

``` javascript

new Date() }
/>
this.props.navigator.pop()}
style={{
backgroundColor: '#3F5C7A',
margin: 10,
}}
textStyle={{color: '#fff'}}>
Done


```

Start by tracing the ModalWidget, its displayValue prop, and DatePickerIOSWidget usage, focusing on how navigator.pop() returns or commits the selected value. Done means the custom Done button closes the modal and the recorded_at display field reflects the selected datetime.

Written by the indexing model from the issue text.