Adjust bsq-swap-offer related gRPC services & msgs
Adjust bsq-swap-offer related gRPC services & msgs

- Adjust GetBsqSwapOffer(s) rpc services to remove currency param.
- Adjust OfferInfo and remove BsqSwapOfferInfo.
- Add GetOfferCategory service so CLI can determine what kind of takeoffer service is to be used.
- Add comment about adding sub-message BsqSwapTradeInfo field to TradeInfo.

bitsquare/bitsquare,bitsquare/bitsquare