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/Podfile.lock

@@ -0,0 +1,22 @@
+PODS:
+  - Flutter (1.0.0)
+  - url_launcher (0.0.1):
+    - Flutter
+
+DEPENDENCIES:
+  - Flutter (from `Flutter`)
+  - url_launcher (from `.symlinks/plugins/url_launcher/ios`)
+
+EXTERNAL SOURCES:
+  Flutter:
+    :path: Flutter
+  url_launcher:
+    :path: ".symlinks/plugins/url_launcher/ios"
+
+SPEC CHECKSUMS:
+  Flutter: 434fef37c0980e73bb6479ef766c45957d4b510c
+  url_launcher: 6fef411d543ceb26efce54b05a0a40bfd74cbbef
+
+PODFILE CHECKSUM: aafe91acc616949ddb318b77800a7f51bffa2a4c
+
+COCOAPODS: 1.10.1