Undefined tags

[staab]

If you call getEditorTags with hints = true, but no hints are available on the nprofile/nevent extensions, undefined gets added to the tags array, and causes events to be invalid. We could default to an empty hint, but relay and pubkey hints are really important, so I think a better approach would be to:

• Add getRelays option to nprofile/nevent extensions so relays can always be populated
• Default to an empty hint if no hints are available
• (optional) I think splitting nprofile/npub and nevent/note would improve things, since currently there's some confusing overloading going on.