Merge #8323: Add HD keypath to CKeyMetadata, report metadata in validateaddress

7945088 [Wallet] comsetic non-code changes for the HD feature (Jonas Schnelli)
68d7682 [Wallet] ensure CKeyMetadata.hdMasterKeyID will be cleared during SetNull() (Jonas Schnelli)
f708085 [QA] extend wallet-hd test to cover HD metadata (Jonas Schnelli)
986c223 [Wallet] print hd masterkeyid in getwalletinfo (Jonas Schnelli)
b1c7b24 [Wallet] report optional HDKeypath/HDMasterKeyId in validateaddress (Jonas Schnelli)
5b95dd2 [Wallet] extend CKeyMetadata with HD keypath (Jonas Schnelli)