Fix loading indicator inconsistency (#9252)

* Use global loading indicator when loading more items

* Use local loading indicator for notifications

And remove global loading indicator for initial custom emojis load

app/javascript/mastodon/features/notifications/index.js

@@ -153,6 +153,7 @@ class Notifications extends React.PureComponent {
         scrollKey={`notifications-${columnId}`}
         trackScroll={!pinned}
         isLoading={isLoading}
+        showLoading={isLoading && notifications.size === 0}
         hasMore={hasMore}
         emptyMessage={emptyMessage}
         onLoadMore={this.handleLoadOlder}