use realtime poll to catch expired/invalid login sessions

assets/js/components/Realtime.js

@@ -27,6 +27,11 @@ class Realtime extends Component {
   fetchData() {
     Client.request(`stats/site/realtime`)
       .then((d) => { this.setState({ count: d })})
+      .catch((e) => {
+        if(e.message === "Unauthorized") {
+          this.props.onError();
+        }
+      })
   }
 
   render(props, state) {

assets/js/pages/dashboard.js

@@ -34,7 +34,7 @@ class Dashboard extends Component {
         <nav class="main-nav animated fadeInDown">
             <ul>
               <li class="logo"><a href="/">Fathom</a></li>
-              <li class="visitors"><Realtime /></li>
+              <li class="visitors"><Realtime onError={this.props.onLogout} /></li>
               <li class="spacer">&middot;</li>
               <li class="signout"><LogoutButton onSuccess={this.props.onLogout} /></li>
           </ul>