add hideBackButtonTitle in order to remove the back button title in the appStyle (#1837)

docs/top-level-api.md

     bottomTabBadgeTextColor: 'red', // Optional, change badge text color. Android only
     bottomTabBadgeBackgroundColor: 'green', // Optional, change badge background color. Android only
     backButtonImage: require('./pathToImage.png') // Change the back button default arrow image with provided image. iOS only
+    hideBackButtonTitle: true/false // Hide back button title. Default is false. If `backButtonTitle` provided so it will take into account and the `backButtonTitle` value will show. iOS only
   },
   drawer: { // optional, add this if you want a side menu drawer in your app
     left: { // optional, define if you want a drawer from the left

ios/RCCNavigationController.m

                      style:navigatorStyle];
     
     NSString *backButtonTitle = actionParams[@"backButtonTitle"];
+    if (!backButtonTitle) {
+      NSNumber *hideBackButtonTitle = [[RCCManager sharedInstance] getAppStyle][@"hideBackButtonTitle"];
+      BOOL hideBackButtonTitleBool = hideBackButtonTitle ? [hideBackButtonTitle boolValue] : NO;
+      backButtonTitle = hideBackButtonTitleBool ? @"" : backButtonTitle;
+    }
+    
     if (backButtonTitle)
     {
       UIBarButtonItem *backItem = [[UIBarButtonItem alloc] initWithTitle:backButtonTitle