Wide Coverage Demo App updates

+ Add Clear button.
+ Use localstorage to remember entered text between visits.
+ Add a link to it on the GF cloud service start page.

src/www/index.html

@@ -20,6 +20,7 @@
   <li><a href="gfse/">GF online editor for simple multilingual grammars</a>
   <li><a href="translator/">Simple Translation Tool</a>
       (bilingual document editor)
+  <li><a href="wc.html">Wide Coverage Translation Demo</a>
 </ul>
 
 <h2>Documentation</h2>