Implement JSON RPC2 interface

[DerAndereAndi]

The task is to coordinate development of JSON RPC2 implementation in https://github.com/enbility/eebus-go/pull/129

These items have been agreed upon:

• [ ] Define Interface API
• [ ] The EEBUS service should not start automatically, instead the option to start & stop should be used
• [ ] Allow only one TCP connection at a time
• [ ] Monitor active TCP connection and automatically call api.ServiceInterface.Shutdown() on disconnect
• [ ] Add JSON parsing support for api.DeviceRemoteInterface and api.EntityRemoteInterface nested in structs (e. g. api.UseCaseBaseInterface.RemoteEntitiesScenarios()
• [ ] ...

Please add your suggestions in comments and lets discuss them.

[randomdudebunchofnumbers]

Some suggestions:

• Remove service autostart
• Allow only one TCP connection at a time
• Monitor active TCP connection and automatically call api.ServiceInterface.Shutdown() on disconnect
• Always return all return parameters
• Add JSON parsing support for api.DeviceRemoteInterface and api.EntityRemoteInterface nested in structs (e. g. api.UseCaseBaseInterface.RemoteEntitiesScenarios()

[sthelen-enqs]

I've created https://github.com/enbility/eebus-go/pull/131 to clean up the return parameters a bit