Feature request: Add getter and autoreconnect for subscriptions

[dsbaars]

I noticed that when the Nostr connection is closed (for example because the WiFi connection dropped), the subscription dropped as well.
Currently there is no way to get the status of subscriptions, it would be great to check if a subscription still exist and if not the application could resubscribe.

Edit: Alternatively or additionally it would be even better to restore subscriptions after restoring the connection.

[riccardobl]

Both requested features have been added in v1.5.0