Better relay access detection

[staab]

Ideally, we will be able to create a spec for requesting and/or querying access as in #6, but short term we should probe relays:

• [x] Test whether AUTH is successful (if no failure comes through treat it as a public relay)
• [x] Warn users if it's a public relay, since it may have spam/objectionable content
• [x] Test whether publish works (send current profile or something)
• [ ] Test whether a REQ works. Maybe load up the space's rooms and kind 1s to see if the relay can support our feature set.