We have a working UI and working backend for cross-wiki notifications, all that's missing is middleware. We need:
- the `meta=notifications` API module to tell the frontend about how many foreign notifications there are, and on which wikis
- but with a parameter to disable this behavior, so we don't get nested foreign notifications in a loop
- the API output needs to include at least the max timestamp of the foreign notifications, so we can the foreign notifications bundle in the right place
- the API output needs to contain the api.php URLs of the relevant foreign wikis, so the UI code can contact them
- the numbers on the badges to reflect foreign notifications
- the badges to be colored when there are unseen foreign notifications (even if all local notifications are seen)