Find a way to cache `POST` requests

[nfoert]

Currently it's not a possible to cache post requests due to a limitation in the cache library. Usually this would not be an issue, as a POST request usually references API data, and it doesn't make sense to cache it. However, when the user is offline, there's certain features that won't work unless the request can be found from the cache (eg. TBA event list). In most cases, it's better to return something, even if it's not the most up to date information.

This could be solved by creating a second layer of the service worker to watch for POST requests and either cache the requests inside of an IndexedDB. This should be network first so it always fetches the latest data

• https://stackoverflow.com/questions/35270702/can-service-workers-cache-post-requests
• Allow Caching of POST requests w3c/ServiceWorker#977