Search Protocol: User.search

[mhchia]

• Recursive search through hubs
• Return a list of proof of indirect connection, not only the first one
• Handle maximum depth of the recursive search
  • tests
• Avoid redundant search through memorizing the seen salt(hubPubkey)
• Proof of Salted Connection
  • Add wire message for it
  • Verify proof of salted connection
  • Reject if proof of salted connection is invalid