GH-4080-wildcard_aens_delegation_signature

• Add generic/wildcard AENS delegation signatures. I.e. instead of delegating authority for a contract to operate with a specific name (name hash), by signing just the string AENS (+ network id, public key and contract address as usual) you can delegate the authority for a contract to handle all your names with one signature. See Issue #4080 for details.

  BEWARE: This gives the contract authority to handle all current and future names on your behalf, so it should be used with extreme care and only for well-known (and well understood!!) contracts.