Add samples index (#359)

* add samples_index to web/ directory

Co-authored-by: Thea Flowers <theaflowers@google.com>

* add pub_get.dart script

* build sample index in peanut post build

* re-generate sample index with web demos

* print more details in peanut_post_build.dart

* add images for demos

* run generator

* update README

* add animations and provider shopper as symlinks

* add links to symlinked web demos

* use relative paths

* update cookbook images, urls, and description CSS

* use relative URL for navbar link

* unstage HTML files

* .gitignore generated HTML files

* add margin to toolbar

* rename escape functions

* add and update copyright headers

Co-authored-by: Thea Flowers <theaflowers@google.com>

web/github_dataviz/pubspec.lock

@@ -14,7 +14,7 @@ packages:
       name: charcode
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.2"
+    version: "1.1.3"
   collection:
     dependency: transitive
     description: