Update Navigation and Routing sample (#851)

* Add duration parameter to FadeTransitionPage

* Use didChangeDependencies instead of didUpdateWidget

* Don't notify listeners if the path hasn't changed

* Update navigation sample WIP

* Use Link and RouteStateScope in settings screen

* update README

* use named parameters for Library.addBook()

* Make _handleAuthStateChanged synchronous

* add missing copyright headers

* Address code review comments

* Address code review comments

navigation_and_routing/lib/main.dart

@@ -10,6 +10,14 @@ import 'src/app.dart';
 void main() {
   // Use package:url_strategy until this pull request is released:
   // https://github.com/flutter/flutter/pull/77103
-  setPathUrlStrategy();
+
+  // Use to setHashUrlStrategy() to use "/#/" in the address bar (default). Use
+  // setPathUrlStrategy() to use the path. You may need to configure your web
+  // server to redirect all paths to index.html.
+  //
+  // On mobile platforms, both functions are no-ops.
+  setHashUrlStrategy();
+  // setPathUrlStrategy();
+
   runApp(const Bookstore());
 }