Update notifications periodically (#311)

- Call periodically from API class

lib/widget/drawer.dart

@@ -129,9 +129,12 @@ class InvenTreeDrawer extends StatelessWidget {
     }
 
     if (InvenTreeAPI().supportsNotifications) {
+      int notification_count = InvenTreeAPI().notification_counter;
+
       tiles.add(
         ListTile(
           leading: FaIcon(FontAwesomeIcons.bell),
+          trailing: notification_count > 0 ? Text(notification_count.toString()) : null,
           title: Text(L10().notifications),
           onTap: _notifications,
         )

lib/widget/home.dart

@@ -42,16 +42,6 @@ class _InvenTreeHomePageState extends State<InvenTreeHomePage> with BaseWidgetPr
     // Initially load the profile and attempt server connection
     _loadProfile();
 
-    _refreshNotifications();
-
-    // Refresh notifications every ~30 seconds
-    Timer.periodic(
-        Duration(
-          milliseconds: 30000,
-        ), (timer) {
-      _refreshNotifications();
-    });
-
     InvenTreeAPI().registerCallback(() {
 
       if (mounted) {
@@ -180,28 +170,6 @@ class _InvenTreeHomePageState extends State<InvenTreeHomePage> with BaseWidgetPr
     setState(() {});
   }
 
-  /*
-   * Refresh the number of active notifications for this user
-   */
-  Future<void> _refreshNotifications() async {
-
-    if (!InvenTreeAPI().isConnected()) {
-      return;
-    }
-
-    // Ignore if the widget is no longer active
-    if (!mounted) {
-      return;
-    }
-
-    // final notifications = await InvenTreeNotification().list();
-
-    setState(() {
-      // _notificationCounter = notifications.length;
-    });
-  }
-
-
   Widget _listTile(BuildContext context, String label, IconData icon, {Function()? callback, String role = "", String permission = "", Widget? trailing}) {
 
     bool connected = InvenTreeAPI().isConnected();