Create `Result` class to hold traverse result edges.

Purpose of suggestion.

GroupBy, OrderBy, Filtering implementation of fetched result edges are spread out multiple parts(Storage, AsynchbaseStorage, PostProcess). It would be much better we can separate post process logic(OrderBy, GroupBy, FilterOut) in `Result` class so any caller simply can benefit single implementation.

In general, I am suggesting changing PostProcess only call method of Result class, not actually implement logic.

I was asked if we can provide binary format(not JSON) such as protobuf, thrift, etc and I think it is reasonable demand. While I was tapping out possibility of this, I found out moving post process implementation into `Result` class can make this really easy, I guess we can simply focus on actual `format` not post process logic itself.