add fps tracker in expert mode

web/kiri/index.css

@@ -1054,3 +1054,10 @@ th, tr, td, label {
     padding: 5px 20px 5px 20px;
     margin-left: 10px;
 }
+#fps {
+    position: fixed;
+    right: 5px;
+    bottom: 5px;
+    font-size: 10px;
+    color: #000;
+}

web/kiri/index.html

@@ -381,6 +381,7 @@
         <p>this site uses cookies to preserve application preferences</p>
         <button id="gotit" class="f-col j-center">got it</button>
     </div>
+    <div id="fps" class="noshow"></div>
 </div>
 </body>
 </html>