Currency: Add missing setters in the DTO
Currency: Add missing setters in the DTO

It was causing regression in versions of Mono prior to 3.12.0
See: https://travis-ci.org/Gatecoin/api-gatecoin-dotnet/builds/202536921

Gatecoin/API_client_csharp,Gatecoin/api-gatecoin-dotnet,Gatecoin/api-gatecoin-dotnet