Add Twitter Bootstrap stylesheet as internal resource to avoid invalid certificate of CDN

templates/layout.latte

@@ -16,7 +16,7 @@
         <base href="{$config['root_url']}/">
         <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=0">
         {ifset #meta}{include meta}{/ifset}
-        <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
+        <link rel="stylesheet" href="css/bootstrap.min.css">
         <link rel="stylesheet" href="css/main.css">
         {ifset #head}{include head}{/ifset}
     </head>