Datasets cached in localStorage

`/datasets` end point is the single source of truth for available datasets provided by the server

- Ensure `/datasets` is used on App start up, unless in offline mode

Start at the App startup path and trace how datasets are loaded from localStorage versus the `/datasets` endpoint. Check the offline-mode branch first. Done means online startup uses `/datasets` as the source of available datasets, while offline mode continues to use the local cache.

Written by the indexing model from the issue text.