Add chat message classes

[aontas]

Adding in chat message alternate form of communication from server -> client.

First draft of adding it to Bloodstone (this form is currently untested, but the theory works). Am after any design changes or updates that I should make.

Tests would be useful to add.

Intended use:

SharedLibrary:

public struct DataPacket : VNetworkChatMessage
{
  string Data;
}

Server:

MessageUtils.OnClientConnectionEvent += (User user) => {
   // Client has connected! woo! now I can send them messages!
}

Client:

MessageUtils.RegisterType<DataPacket>((DataPacket message) => {
  // I have received this message. Need to cast it into appropriate type
});

// After client has sufficiently loaded to be able to receive messages
MessageUtils.InitialiseClient();

[aontas]

Feel free to request anything to move around or whatever. I not really sure where things are supposed to go (Should the ClientChat be in Hooks, or be in Network alongside SerialisationHooks?)