Add constant BTCChinaExchange.DEFAULT_MARKET.
Implement BTCChina buyIcebergOrder and sellIcebergOrder API methods.
Implement BTCChina cancelIcebergOrder API method.
Implement BTCChina getIcebergOrder and getIcebergOrders API methods.
Change order ID type from long to int, to make consistent.
Merge pull request #550 from sutra/develop

Implement BTCChina Trade API v1.7