WebUI: Select username on login page load

On logout, the input field is not empty. Select its content.

src/webui/www/private/login.html

@@ -9,6 +9,7 @@
     <script type="text/javascript">
       window.onload = function() {
         $('username').focus();
+        $('username').select();
       }
 
       window.addEvent('domready', function() {