implement linkREF server

[blairmunroakusa]

linkREF is the process of validating an invite key to connect a dedicated REF account to the recipient's PIECE or MAIN.

server flow will go:
. validate tx
. intake and process invite key
. generate SHA256 hash from key
. compare hash to REF target
. if hash == target, target => invitee address
. transfer all accumulated lamps in REF