Execute Animated.js declarative animation on UIThread on Android.

Summary:This is the first from the series of PRs I'm going to be sending shorty that would let Animated.js animations to run off the JS thread (for Android only).

This PR introduce a new native module that will be used for offloading animations - NativeAnimatedModule. It has a simple API that allows for animated nodes management via methods like: create/drop animated node, connect/disconnect nodes, start animation of a value node, attach/detach animated from a native view.

Similarly to how we handle UIManager view hierarchy updates we create a queue of animated graph operations that are then executed on the UI thread. This isolates us from problems that may be caused by concurrent updates of animated graph while UI thread is "executing" the animation.

The most important class NativeAnimatedNodesManager.java implements a management interface for animated nodes graph as well as implements a graph traversal algorithm that is run for each animation frame. For each animation frame we visit animated nodes th
Closes https://github.com/facebook/react-native/pull/6466

Differential Revision: D3092739

Pulled By: astreet

fb-gh-sync-id: 665b49900b7367c91a93b9d8864f78fb90bb36ba
shipit-source-id: 665b49900b7367c91a93b9d8864f78fb90bb36ba

ReactAndroid/src/main/java/com/facebook/react/uimanager/UIManagerModule.java

@@ -83,6 +83,14 @@ public class UIManagerModule extends ReactContextBaseJavaModule implements
     reactContext.addLifecycleEventListener(this);
   }
 
+  /**
+   * This method gives an access to the {@link UIImplementation} object that can be used to execute
+   * operations on the view hierarchy.
+   */
+  public UIImplementation getUIImplementation() {
+    return mUIImplementation;
+  }
+
   @Override
   public String getName() {
     return "RKUIManager";