added setStackRoot animation support (#3722)

lib/ios/RNNCommandsHandler.m

 	RNNNavigationOptions* options = [newVC getLeafViewController].options;
 	UIViewController *fromVC = [_store findComponentForId:componentId];
 	__weak typeof(RNNEventEmitter*) weakEventEmitter = _eventEmitter;
-	[_stackManager setStackRoot:newVC fromViewController:fromVC animated:options.animations.push.enable completion:^{
+	[_stackManager setStackRoot:newVC fromViewController:fromVC animated:options.animations.setStackRoot.enable completion:^{
 		[weakEventEmitter sendOnNavigationCommandCompletion:setStackRoot params:@{@"componentId": componentId}];
 		completion();
 	} rejection:rejection];

lib/ios/RNNTransitionsOptions.h

 @property (nonatomic, strong) RNNScreenTransition* pop;
 @property (nonatomic, strong) RNNScreenTransition* showModal;
 @property (nonatomic, strong) RNNScreenTransition* dismissModal;
+@property (nonatomic, strong) RNNScreenTransition* setStackRoot;
 
 @end

playground/src/screens/PushedScreen.js

           previousScreenIds: _.concat([], this.props.previousScreenIds || [], this.props.componentId)
         },
         options: {
-          animated: true,
+          animations: {
+            setStackRoot: {
+              enable: false
+            }
+          },
           topBar: {
             title: {
               text: `Pushed ${this.getStackPosition() + 1}`