Save email verification token to person's pod

[mrkvon]

To do this, person has to prepare their pod by creating a settings file that notification service identity has write or append access to. The service also needs read access to every file that participates in the discovery, in particular personal hospex profile.

The settings are discovered as follows:

1. we start with person's webId
2. we fetch (extended) profile and find public type index
3. in public type index, we find resources that are relevant in this particular context (e.g. personal hospex document in case of sleepy.bike)
4. in these resources, we find settings by searching triple <webId> space:preferencesFile <settings> .
5. • to write verification token, we pick the settings which notification service identity has access to, using WAC-Allow header
   • to read verification token, we look for triple <webId> <https://example.com/emailVerificationToken> "token" .
     the predicate for token discovery is editable in config, but should be kept consistent