Update specifications to reflect proposal 350-remote-tap
- Mark proposal 350 as accepted.
- Choose protovers for new desc/microdesc versions.
- Clarify role for Relay=1 protover.
- Mark onion-key and onion-key-crosscert as optional-ish.
- Document publish-dummy-tap-key.
- Describe "CREATE", "CREATED", "EXTEND" and "EXTENDED" as "obsolete".
Additonally:
- Move a note about a tailing = sign into the correct place in the microdesc documentation.