backButtonHidden support

lib/ios/RNNTopBarOptions.h

 @property (nonatomic, strong) NSString* testID;
 @property (nonatomic, strong) RNNTitleOptions* title;
 @property (nonatomic, strong) NSNumber* backButtonImage;
+@property (nonatomic, strong) NSNumber* backButtonHidden;
 @property (nonatomic, strong) NSString* backButtonTitle;
 
 @property (nonatomic, strong) NSString* componentName;

lib/ios/RNNTopBarOptions.m

 		
 		viewController.navigationItem.backBarButtonItem = backItem;
 	}
+	
+	viewController.navigationItem.hidesBackButton = [self.backButtonHidden boolValue];
+	
 }
 
 -(void)storeOriginalTopBarImages:(UIViewController*)viewController {