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/samples_index/web/description.dart

@@ -0,0 +1,10 @@
+import 'dart:html';
+
+import 'package:mdc_web/mdc_web.dart';
+
+InputElement searchInput;
+
+void main() {
+ querySelectorAll('.mdc-card__primary-action')
+      .forEach((el) => MDCRipple(el));
+}