Support multiple servercontexts

[Askaholic]

Refactors the server broadcasting code so that multiple ServerContext's can be run correctly at the same time. This will allow us to start working on a v2 version of the protocol which can concurrently with the legacy protocol. As a sample I've added a SimpleJsonProtocol class that sends each message as a json object followed by a newline.

I think we should try to transition to the new protocol incrementally. As a first step, we can swap out the "transport" or "wire" layer from QDataStream to Json, and keep everything else the same. We could implement this in the client and start using it immediately, which would cut the amount of network traffic in half (due to the legacy protocol using utf-16 encoding instead of utf-8). There isn't really a down side to doing this, as we can keep adding new incremental protocol versions on new ports. Hopefully with these refactors it will even be possible to implement a websocket protocol, but I haven't looked into the details of that yet. I just know that there is a websockets library in python that uses asyncio.

[cleborys]

Very cool how relatively few changes this needed now!

If there were multiple instances with e.g. different player services, would the player services be distinguishable in the logs?
Should there be tests for having multiple instances?

[Askaholic]

If there were multiple instances, you wouldn't be able to tell the difference in the log. Mostly i didn't bother with that since I really don't know why we would ever be running multiple server instances in the same process. I had considered actually forcing the ServerInstance to be a singleton through a metaclass, but decided it was probably overkill to code that in :P.