[iOS/Android] Add initialTabIndex support (#1674)

* Add initialTabIndex support to RCCTabBarController

* Add initialTabIndex support to BottomTabsLayout

android/app/src/main/java/com/reactnativenavigation/layouts/BottomTabsLayout.java

         addScreenStacks();
         createSnackbarContainer();
         showInitialScreenStack();
+        setInitialTabIndex();
+    }
+
+    private void setInitialTabIndex() {
+        if (params.initialTabIndex == null) {
+            return;
+        }
+        bottomTabs.setCurrentItem(params.initialTabIndex);
     }
 
     private void createSideMenu() {

android/app/src/main/java/com/reactnativenavigation/params/ActivityParams.java

     public List<ScreenParams> tabParams;
     public SideMenuParams leftSideMenuParams;
     public SideMenuParams rightSideMenuParams;
+    public Integer initialTabIndex;
     public boolean animateShow;
 }

android/app/src/main/java/com/reactnativenavigation/params/parsers/ActivityParamsParser.java

         }
 
         result.animateShow = params.getBoolean("animateShow", true);
+        result.initialTabIndex = params.getInt("initialTabIndex");
 
         return result;
     }

ios/RCCTabBarController.m

   
   // replace the tabs
   self.viewControllers = viewControllers;
+
+  
+   NSUInteger *initialTabIndex = [props[@"initialTabIndex"] unsignedIntegerValue];
+   if (initialTabIndex && initialTabIndex < viewControllers.count) {
+      [self setSelectedIndex:initialTabIndex];
+   }
   
   [self setRotation:props];
   

src/deprecated/platformSpecificDeprecated.ios.js

         <TabBarControllerIOS
           id={controllerID + '_tabs'}
           style={params.tabsStyle}
-          appStyle={params.appStyle}>
+          appStyle={params.appStyle}
+          initialTabIndex={params.initialTabIndex}>
           {
             params.tabs.map(function(tab, index) {
               return (