Worker io refactor2

Implementation of the receiving (worker) side of the Json over standard IO refactor to use the IWorker interface.
@intern-felicco @abnanda1 @davidfowl 

The reference to the list is readonly, not the contents of the list itself. This means we can't do something like
```cs
_clients = new List<Client>{client};
```
but calling _clients.Add(client) is perfectly acceptable.