Client-side ranking to more efficiently show people stories in feed

Introduced a new client-side ranking architecture for News Feed. This architecture allows stories to be re-ranked on the client after being sent from the server, ensuring that stories with fully-loaded media are prioritized and that users see relevant content more quickly, even on slow network connections. This avoids spinners and gray boxes by requiring stories to have all necessary media available before rendering and by optimizing content for each session.