Implemented automatic IP detection for iOS

Summary:
Implemented automatic IP detection for iOS, based on #6345 and #6362.
As the previous pull requests did, this works by writing the IP address of the host to a file.
Closes facebook/react-native#8091

Differential Revision: D3427657

Pulled By: javache

fbshipit-source-id: 3f534c9b32c4d6fb9615fc2e2c3c3aef421454c5

generator-ios/templates/app/AppDelegate.m

@@ -9,6 +9,7 @@
 
 #import "AppDelegate.h"
 
+#import "RCTBundleURLProvider.h"
 #import "RCTRootView.h"
 
 @implementation AppDelegate
@@ -17,31 +18,7 @@ - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(
 {
   NSURL *jsCodeLocation;
 
-  /**
-   * Loading JavaScript code - uncomment the one you want.
-   *
-   * OPTION 1
-   * Load from development server. Start the server from the repository root:
-   *
-   * $ npm start
-   *
-   * To run on device, change `localhost` to the IP address of your computer
-   * (you can get this by typing `ifconfig` into the terminal and selecting the
-   * `inet` value under `en0:`) and make sure your computer and iOS device are
-   * on the same Wi-Fi network.
-   */
-
-  jsCodeLocation = [NSURL URLWithString:@"http://localhost:8081/index.ios.bundle?platform=ios&dev=true"];
-
-  /**
-   * OPTION 2
-   * Load from pre-bundled file on disk. The static bundle is automatically
-   * generated by the "Bundle React Native code and images" build step when
-   * running the project on an actual device or running the project on the
-   * simulator in the "Release" build configuration.
-   */
-
-//   jsCodeLocation = [[NSBundle mainBundle] URLForResource:@"main" withExtension:@"jsbundle"];
+  jsCodeLocation = [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index.ios" fallbackResource:nil];
 
   RCTRootView *rootView = [[RCTRootView alloc] initWithBundleURL:jsCodeLocation
                                                       moduleName:@"<%= name %>"