navigator.setSubTitle() support for iOS (#1167)

Add setSubTitle implementation for iOS + docs

docs/screen-api.md

 });
 ```
 
+
+## setSubTitle(params = {})
+
+Set the nav bar subtitle dynamically. If your subtitle doesn't change during runtime, set it when the screen is defined / pushed.
+
+```js
+this.props.navigator.setSubTitle({
+  subtitle: "Connecting..." 
+});
+```
+
 ## toggleDrawer(params = {})
 
 Toggle the side menu drawer assuming you have one in your app.

ios/Helpers/RCCTitleViewHelper.h

 - (instancetype)init:(UIViewController*)viewController
 navigationController:(UINavigationController*)navigationController
                title:(NSString*)title subtitle:(NSString*)subtitle
-      titleImageData:(id)titleImageData;
+      titleImageData:(id)titleImageData
+       isSetSubtitle:(BOOL)isSetSubtitle;
 
 -(void)setup:(NSDictionary*)style;
 

ios/Helpers/RCCTitleViewHelper.m

 @property (nonatomic, strong) NSString *title;
 @property (nonatomic, strong) NSString *subtitle;
 @property (nonatomic, strong) id titleImageData;
+@property (nonatomic) BOOL isSetSubtitle;
 
 @property (nonatomic, strong) RCCTitleView *titleView;
 
 navigationController:(UINavigationController*)navigationController
                title:(NSString*)title subtitle:(NSString*)subtitle
       titleImageData:(id)titleImageData
+       isSetSubtitle:(BOOL)isSetSubtitle
+
 {
     self = [super init];
     if (self) {
         self.viewController = viewController;
         self.navigationController = navigationController;
-        self.title = [RCCTitleViewHelper validateString:title];
+        if(isSetSubtitle){
+            self.title = viewController.navigationItem.title;
+        } else {
+            self.title = [RCCTitleViewHelper validateString:title];
+        }
         self.subtitle = [RCCTitleViewHelper validateString:subtitle];
         self.titleImageData = titleImageData;
     }

ios/RCCNavigationController.m

                   props:(NSDictionary*)props
                   style:(NSDictionary*)style
 {
-  
+  BOOL isSetSubtitleBool = props[@"isSetSubtitle"] ? [props[@"isSetSubtitle"] boolValue] : NO;
   RCCTitleViewHelper *titleViewHelper = [[RCCTitleViewHelper alloc] init:viewController
                                                     navigationController:self
                                                                    title:props[@"title"]
                                                                 subtitle:props[@"subtitle"]
-                                                          titleImageData:props[@"titleImage"]];
+                                                          titleImageData:props[@"titleImage"]
+                                                           isSetSubtitle:isSetSubtitleBool];
   
   [titleViewHelper setup:style];
   

ios/RCCViewController.m

   if (self.navigationItem.titleView && [self.navigationItem.titleView isKindOfClass:[RCCTitleView class]]) {
     
     RCCTitleView *titleView = (RCCTitleView *)self.navigationItem.titleView;
-    RCCTitleViewHelper *helper = [[RCCTitleViewHelper alloc] init:viewController navigationController:viewController.navigationController title:titleView.titleLabel.text subtitle:titleView.subtitleLabel.text titleImageData:nil];
+    RCCTitleViewHelper *helper = [[RCCTitleViewHelper alloc] init:viewController navigationController:viewController.navigationController title:titleView.titleLabel.text subtitle:titleView.subtitleLabel.text titleImageData:nil isSetSubtitle:NO];
     [helper setup:self.navigatorStyle];
   }
   

src/deprecated/platformSpecificDeprecated.ios.js

     title: params.title,
     subtitle: params.subtitle,
     titleImage: params.titleImage,
-    style: params.navigatorStyle
+    style: params.navigatorStyle,
+    isSetSubtitle: false
+  });
+}
+
+function navigatorSetSubtitle(navigator, params) {
+  Controllers.NavigationControllerIOS(navigator.navigatorID).setTitle({
+    title: params.title,
+    subtitle: params.subtitle,
+    titleImage: params.titleImage,
+    style: params.navigatorStyle,
+    isSetSubtitle: true
   });
 }
 
   dismissInAppNotification,
   navigatorSetButtons,
   navigatorSetTitle,
+  navigatorSetSubtitle,
   navigatorSetStyle,
   navigatorSetTitleImage,
   navigatorToggleDrawer,