phase3(critical-path): home page chain null-safe

home.dart + desktop/mobile navigation, carousels, index content widgets,
customers_logo, appbar_menu, navigation_drawer, MobileBottomNav, double_back.
Fixes: Key? params, nullable State fields, Scrollbar thumbVisibility,
ModalRoute.of()?, badges hide Badge, cartInfos local promotion.

lib/widgets/mobile/mobile_navigationbar.dart

@@ -10,11 +10,12 @@ import '../../widgets/general/navigationbar_logo.dart';
 import '../../routes.dart';
 
 class MobileNavigationBar extends StatefulWidget {
-  final String title;
-  final bool back;
-  final bool toHome;
-  final bool showMe;
-  const MobileNavigationBar({Key key, this.title, this.back, this.toHome, this.showMe}) : super(key: key);
+  final String? title;
+  final bool? back;
+  final bool? toHome;
+  final bool? showMe;
+
+  const MobileNavigationBar({Key? key, this.title, this.back, this.toHome, this.showMe}) : super(key: key);
 
   @override
   State<StatefulWidget> createState() {
@@ -24,19 +25,19 @@ class MobileNavigationBar extends StatefulWidget {
 }
 
 class MobileNavigationBarState extends State<MobileNavigationBar> {
-  User _user;
+  User? _user;
 
   @override
   Widget build(BuildContext context) {
     return AppBar(
-      leading: widget.back ?
+      leading: widget.back == true ?
       IconButton(
         icon: Icon(
           Icons.arrow_back_ios,
           color: Colors.white,
         ),
         onPressed: () {
-          if (widget.toHome) {
+          if (widget.toHome == true) {
             Routes.router.navigateTo(context, '/', clearStack: true);
           } else {
             Routes.router.pop(context);
@@ -53,7 +54,7 @@ class MobileNavigationBarState extends State<MobileNavigationBar> {
         },
       ),
       title: Container(
-        child: widget.title.isNotEmpty ?
+        child: widget.title?.isNotEmpty == true ?
         Container(
           child: Text(
             '${widget.title}',