Generate bundle and assets when building via Xcode

Summary: This integrates React Native into Xcode's build process, which lets us automatically handle bundling and packaging image assets.

Tested the script via https://github.com/frantic/ReactNativeAssetsExample

Loaded from packager:
<img width="432" alt="screen shot 2015-10-19 at 3 11 12 pm" src="https://cloud.githubusercontent.com/assets/192222/10593447/be5bc7e8-7678-11e5-8c70-ecc2a1ee24fc.png">

Loaded from offline bundle:
<img width="432" alt="screen shot 2015-10-19 at 3 10 58 pm" src="https://cloud.githubusercontent.com/assets/192222/10593448/be5d5194-7678-11e5-8b02-d492a26cfb81.png">

Android:
<img width="639" alt="screen shot 2015-10-19 at 3 11 20 pm" src="https://cloud.githubusercontent.com/assets/192222/10593449/be5de2d0-7678-11e5-8d3c-0378fc447f15.png">
Closes https://github.com/facebook/react-native/pull/3523

Reviewed By: mkonicek

Differential Revision: D2557923

Pulled By: frantic

fb-gh-sync-id: 19957e255993696e793b0162662772efd89f5c1a

react-native-xcode.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+# Copyright (c) 2015-present, Facebook, Inc.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree. An additional grant
+# of patent rights can be found in the PATENTS file in the same directory.
+
+# Bundle React Native app's code and image assets.
+# This script is supposed to be invoked as part of Xcode build process
+# and relies on envoronment variables (including PWD) set by Xcode
+
+case "$CONFIGURATION" in
+  Debug)
+    DEV=true
+    ;;
+  Release)
+    DEV=false
+    ;;
+  "")
+    echo "$0 must be invoked by Xcode"
+    exit 1
+    ;;
+  *)
+    echo "Unsupported value of \$CONFIGURATION=$CONFIGURATION"
+    exit 1
+    ;;
+esac
+
+# Xcode project file for React Native apps is located in ios/ subfolder
+cd ..
+
+set -x
+DEST=$CONFIGURATION_BUILD_DIR/$UNLOCALIZED_RESOURCES_FOLDER_PATH
+
+react-native bundle \
+  --entry-file index.ios.js \
+  --platform ios \
+  --dev $DEV \
+  --bundle-output "$DEST/main.jsbundle" \
+  --assets-dest "$DEST"