Add loading indicator for notifications, make timelines indicate bottoming out when no more statuses

src/services/timeline_fetcher/timeline_fetcher.service.js

@@ -35,6 +35,7 @@ const fetchAndUpdate = ({store, credentials, timeline = 'friends', older = false
         store.dispatch('queueFlush', { timeline: timeline, id: timelineData.maxId })
       }
       update({store, statuses, timeline, showImmediately, userId})
+      return statuses
     }, () => store.dispatch('setError', { value: true }))
 }