Add MapView annotation callback when it gets / lost the focus

Summary:
For my project it was required to receive a notification when the MapView annotation was deselected.

So I renamed `onAnnotationPress` to `onAnnotationSelected` and added a new method `onAnnotationDeselected`, this names was "inspired" by the underlaying iOS API. The old API was still called and marked as deprecated.

But maybe you have an idea for a better naming (onAnnotationFocus/-Blur?) -- or should a deselected call the press method again without an annotation (undefined)?
Closes https://github.com/facebook/react-native/pull/5167

Reviewed By: svcscm

Differential Revision: D2869695

Pulled By: nicklockwood

fb-gh-sync-id: 91795ac3f1e4533b250af8901534d8870729d9db

Examples/UIExplorer/MapViewExample.js

@@ -320,6 +320,20 @@ exports.examples = [
       }}/>;
     }
   },
+  {
+    title: 'Annotation focus example',
+    render() {
+      return <AnnotationExample style={styles.map} annotation={{
+        title: 'More Info...',
+        onFocus: () => {
+          alert('Annotation gets focus');
+        },
+        onBlur: () => {
+          alert('Annotation lost focus');
+        }
+      }}/>;
+    }
+  },
   {
     title: 'Draggable pin',
     render() {