Implement ping-pong flow in the chat actor using current parser

[ygunayer]

Our chat actor currently parses the incoming TcpStream on its own, but this is sub-optimal. We need to borrow this logic from the current parser, which in turn will be replaced with a separate codec phase when #2 is done.

We still think that the ChatIOActor should keep its role as the supervisor and I/O gateway for the ChatActor itself, so the process of capturing the string from the TcpStream, passing it through the parser, and sending properly parsed commands to the ChatActor should be handled in the ChatIOActor as well.

Likewise, the act of receiving commands or messags from the ChatActor, and converting them to a string through the codec library should be the ChatIOActor's responsibility too.