chore: rename modules/examples to modules/playground

The directory contains code authored in a style that makes it transpilable to dart. As such, these are not idiomatic examples of Angular 2 usage.

The main purpose of this directory is to enable experimentation with Angular within the angular/angular repository.

Closes #4342

Closes #4639

modules/playground/src/routing/drafts.html

@@ -0,0 +1,11 @@
+<div ng-if="ready">
+  <h2 class="page-title">Drafts</h2>
+
+  <ol class="inbox-list">
+    <li *ng-for="#item of items" class="inbox-item-record">
+      <a id="item-{{ item.id }}"
+         [router-link]="['/DetailPage', {'id':item.id}]">
+        {{ item.subject }}</a>
+    </li>
+  </ol>
+</div>