[FEATURE] Add gosdk API wrappers to an interface

[Sriep]

Add gosdk API wrappers to an interface object. Similar to TransactionScheme but for zboxcore/sdk..

This would help for 3rd party applications, like zbox and zwallet, that use gosdk. They could then use the interface object rather than the raw functions, if nothing else it would make unit tests easier to write.

So an interface object that has as methods at least the gosdk API functions used in zbox and zwallet, and an object that satisfies the interface and wraps the existing functions.