RPC: New RPC command "submitheader"
RPC: New RPC command "submitheader"

Backport from Novo

nlgcoin/guldencoin-official,nlgcoin/guldencoin-official,nlgcoin/guldencoin-official,nlgcoin/guldencoin-official,nlgcoin/guldencoin-official,nlgcoin/guldencoin-official