Replace navigation_and_routing with a new sample (#832)

* move snippets into old_snippets directory

* add new navigation_and_routing sample

* add copyright headers

* Apply #827 to old_snippets/ directory and upgrade them to null safety

* Code review comments

- Move Guard class into parser.dart
- Move usage of guards from Delegate to RouteInformationParser
- Rename delegate to SimpleRouterDelegate

* clean up imports

* refactor settings screen, fix bug

* avoid conflicting paths /books/new and /books/1 - rename to book/1

* dispose fields in _BookstoreState class

* remove /books path

This was causing problems

* add comment

* Change BookstoreAuthScope and BookstoreAuthScope to InheritedNotifier

* fix warnings

* Make the initial route configurable, set to '/signin'

* Enable deep linking

https://flutter.dev/docs/development/ui/navigation/deep-linking

* use path URL strategy on the web.

* remove TODO, add comment

navigation_and_routing/ios/Runner/Info.plist

@@ -11,7 +11,7 @@
 	<key>CFBundleInfoDictionaryVersion</key>
 	<string>6.0</string>
 	<key>CFBundleName</key>
-	<string>navigation_and_routing</string>
+	<string>bookstore</string>
 	<key>CFBundlePackageType</key>
 	<string>APPL</string>
 	<key>CFBundleShortVersionString</key>
@@ -41,5 +41,20 @@
 	</array>
 	<key>UIViewControllerBasedStatusBarAppearance</key>
 	<false/>
+	<key>FlutterDeepLinkingEnabled</key>
+    <true/>
+    <key>CFBundleURLTypes</key>
+    <array>
+        <dict>
+        <key>CFBundleTypeRole</key>
+        <string>Editor</string>
+        <key>CFBundleURLName</key>
+        <string>flutterbooksample.com</string>
+        <key>CFBundleURLSchemes</key>
+        <array>
+        <string>customscheme</string>
+        </array>
+        </dict>
+    </array>
 </dict>
 </plist>