Move all distribution assets to separate folder

html/index.html

@@ -8,7 +8,7 @@
         <!--[if lt IE 9]>
           <script src="http://html5shim.googlecode.com/svn/trunk/html5.js"></script>
         <![endif]-->
-        <link href="bootstrap.min.css" rel="stylesheet" />
+        <link href="assets/bootstrap.min.css" rel="stylesheet" />
         <style>
             input#serial_id, div#answer { font-family: monospace }
         </style>