Several improvements to StackNavigation Header (#3568)

* Refactor to remove unused variables, styles, and outer Animated view

* Style cleanup

* Proof of concept blur background

* Clean it up and add flow interface

* Update snapshots

examples/NavigationPlayground/js/SimpleStack.js

@@ -178,20 +178,18 @@ MyProfileScreen.navigationOptions = props => {
   };
 };
 
-const SimpleStack = StackNavigator(
-  {
-    Home: {
-      screen: MyHomeScreen,
-    },
-    Profile: {
-      path: 'people/:name',
-      screen: MyProfileScreen,
-    },
-    Photos: {
-      path: 'photos/:name',
-      screen: MyPhotosScreen,
-    },
-  }
-);
+const SimpleStack = StackNavigator({
+  Home: {
+    screen: MyHomeScreen,
+  },
+  Profile: {
+    path: 'people/:name',
+    screen: MyProfileScreen,
+  },
+  Photos: {
+    path: 'photos/:name',
+    screen: MyPhotosScreen,
+  },
+});
 
 export default SimpleStack;