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.
