Add pep_publish testcase stub
Send client disco#info
Publish an event and expect the notification
Use a static id to make the client identifiable
Print clients' states
Don't litter the logs/wire with unnecessary registrations
Subscribe Bob to Alice's presence updates
Extract `subscribe/2`
Subscribe Alice to Bob's presence updates

It's Bob whose presence must reach Alice.
The presence stanza contains the announcement of interest in Alice's
PEP notifications.
Make pep_publish pass (needs cleanup!)

Right now this will work only once the fake caps are already cached,
i.e. the `ver` attr is known to the server.