Notification sounds (#367)

* Basic notification sound support

* Add settings option for notification sounds

* Allow sound without desktop notifications

src/client/action/settings.js

@@ -36,3 +36,9 @@ export function toggleNotifications() {
     type: cons.actions.settings.TOGGLE_NOTIFICATIONS,
   });
 }
+
+export function toggleNotificationSounds() {
+  appDispatcher.dispatch({
+    type: cons.actions.settings.TOGGLE_NOTIFICATION_SOUNDS,
+  });
+}