Open-source ART for Android

Summary:
This is already open-source on iOS, albeit badly documented. Now Android too!

Tested in open source by adding a `import com.facebook.react.ARTPackage;` and `.addPackage(new ARTPackage())` to UIExplorerActivity.java, running

```
./gradlew :Examples:UIExplorer:android:app:installDebug
```

and copying VectorWidget into the UIExplorer JS code as described in http://browniefed.com/blog/2015/05/03/getting-react-art-running-on-react-native/.

public

Reviewed By: foghina

Differential Revision: D2700481

fb-gh-sync-id: 2a5308b022869ecc1868a46dbecf397581ddbe04

ReactAndroid/src/main/java/com/facebook/react/shell/MainReactPackage.java

@@ -27,6 +27,8 @@ import com.facebook.react.modules.storage.AsyncStorageModule;
 import com.facebook.react.modules.toast.ToastModule;
 import com.facebook.react.modules.websocket.WebSocketModule;
 import com.facebook.react.uimanager.ViewManager;
+import com.facebook.react.views.art.ARTRenderableViewManager;
+import com.facebook.react.views.art.ARTSurfaceViewManager;
 import com.facebook.react.views.drawer.ReactDrawerLayoutManager;
 import com.facebook.react.views.image.ReactImageManager;
 import com.facebook.react.views.progressbar.ReactProgressBarViewManager;
@@ -74,6 +76,10 @@ public class MainReactPackage implements ReactPackage {
   @Override
   public List<ViewManager> createViewManagers(ReactApplicationContext reactContext) {
     return Arrays.<ViewManager>asList(
+      ARTRenderableViewManager.createARTGroupViewManager(),
+      ARTRenderableViewManager.createARTShapeViewManager(),
+      ARTRenderableViewManager.createARTTextViewManager(),
+      new ARTSurfaceViewManager(),
       new ReactDrawerLayoutManager(),
       new ReactHorizontalScrollViewManager(),
       new ReactImageManager(),