Add SteemUSD: support thread

I have a ticker symbol and the name. The name is flexible to get changed later but the ticker symbol not. It is like an ID and used for lookup market price at the price feed providers (poliniex, btcaverage).
BITUSD and BITCNY is at poloniex used as ticker. So I stick with that. STEEEMUSD we dont get the feed as they use SBD.