Implement automatic engine channel configuration for EngineResult

[thrau]

Currently engine results are never returned to the client, because we first implemented the Recorder engine, and there's no result to return.
To implement #15, we need to return EngineResult instances to the client. The client also needs to accept them.
In the current situation there are channels that return results and some that don't. That needs to be dynamically configured at runtime when channels are created.

In the go implementation this will manifest in properly implementing and instantiating an EngineResultWriter.
In python we will have to add new abstractions.

• write engine results to socket
• specify schema of specific EngineResult in the EngineSpec
• deserialize EngineResult correctly