Lightbox can receive onLongPress function as a prop. (#108)

* Included onLongPress

* Lightbox can now handle onLongPress event

* Adjusted default behaviour to null

* Move onLongPress to static defaultProps

* Renamed package

* Revert name change

Author: TomJamesDuffy

Lightbox.js

@@ -28,6 +28,7 @@ export default class Lightbox extends Component {
     didOpen: () => {},
     willClose: () => {},
     onClose: () => {},
+    onLongPress: () => {},
   };
 
   state = {
@@ -129,6 +130,7 @@ export default class Lightbox extends Component {
           <TouchableHighlight
             underlayColor={this.props.underlayColor}
             onPress={this.open}
+            onLongPress={this.props.onLongPress}
           >
             {this.props.children}
           </TouchableHighlight>