Adds a 'Publish to Nostr' fieldset to node forms, protected by the

'publish to nostr network' permission. It currently assumes the content of

your post is stored in the 'body' field, but this can be overridden by a

setting.

Once the node has been sent, you can't publish it anymore. The event id is

stored in the nostr_simple_publish table.

There's an extra permission to view debug information after trying to post to

the network.