tipe email, more mobile firendly

src/templates/login_panel.html

 <form id="converse-login" method="post">
     <label>{{label_username}}</label>
-    <input type="username" name="jid" placeholder="user@server">
+    <input type="email" name="jid" placeholder="user@server">
     <label>{{label_password}}</label>
     <input type="password" name="password" placeholder="password">
     <input class="submit" type="submit" value="{{label_login}}">