RN Android: Support View Manager Commands that are strings

Summary:
Right now JS triggers a view manager command with the following code:

```
UIManager.dispatchViewManagerCommand(
  ReactNative.findNodeHandle(this),
  UIManager.getViewManagerConfig('RCTView').Commands.hotspotUpdate,
  [destX || 0, destY || 0],
);
```

As we want to get rid of calls to UIManager, we need to stop looking for the integer defined in native from JavaScript. We will be changing methods like this to be:

```
UIManager.dispatchViewManagerCommand(
  ReactNative.findNodeHandle(this),
  'hotspotUpdate',
  [destX || 0, destY || 0],
);
```

We need to support ints and Strings to be backwards compatible, but ints will be deprecated.

Reviewed By: shergin

Differential Revision: D15955444

fbshipit-source-id: d1c488975ae03404f8f851a7035b58a90ed34163

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

@@ -172,6 +172,18 @@ public abstract class ViewManager<T extends View, C extends ReactShadowNode>
   public void receiveCommand(@Nonnull T root, int commandId, @Nullable ReadableArray args) {
   }
 
+  /**
+   * Subclasses may use this method to receive events/commands directly from JS through the
+   * {@link UIManager}. Good example of such a command would be {@code scrollTo} request with
+   * coordinates for a {@link ScrollView} instance.
+   *
+   * @param root View instance that should receive the command
+   * @param commandId code of the command
+   * @param args optional arguments for the command
+   */
+  public void receiveCommand(@Nonnull T root, String commandId, @Nullable ReadableArray args) {
+  }
+
   /**
    * Subclasses of {@link ViewManager} that expect to receive commands through
    * {@link UIManagerModule#dispatchViewManagerCommand} should override this method returning the