Update element pages to make not of PolymerLabs.

- pages are not an expandable list of elements
- prep for core-* elements inclusion

_includes/labs.html

@@ -0,0 +1,4 @@
+<p class="alert alert-error">
+  <polymer-ui-icon src="/images/picons/ic_notification_error_dark_.png" style="background-size:30px !important;"></polymer-ui-icon>
+  <b>Things may break!</b> This material is part of <a href="https://github.com/PolymerLabs">PolymerLabs</a>, our testing ground for experimental stuff. APIs, documentation, and demos may not be actively maintained.
+</p>

_includes/toc.html

@@ -1,7 +1,7 @@
 {%comment%}
-  The GENERATED_TOC_START and GENERATED_TOC_END signify the start and end
+  The TOC_START and TOC_END signify the start and end
   of the generated TOC. Used in process_toc.rb to wrap the content in a
-  <detail> element.
+  `<detail>` element.
 {%endcomment%}
 
 <!--TOC_START-->

docs/elements/core-elements.md

@@ -0,0 +1,24 @@
+---
+layout: default
+type: elements
+navgroup: docs
+shortname: Elements
+title: Core elements
+subtitle: non-visual utility elements
+
+add_permalinks: false
+
+stylesheets:
+  "/css/elementpage.css"
+---
+
+**Note:** These elements and their documentation are still early. The "source" links below point to commented code where you can learn more about how to use the element.
+{: .alert .alert-info}
+
+Install everything:
+
+    bower install Polymer/core-elements
+
+<section class="element-list">
+{% directory org:Polymer dir:components tag:div glob:core-* blacklist:"core-elements core-component-page-dev" %}
+</section>