multiplayer: names instead of peer numbers, a chat, and the exe as a dedicated server

Three things that turn out to be one thing: a session with people in it needs
to be able to say who they are, and a machine that only referees one should not
have to open a window to do it.

Names. A peer id is what the protocol addresses; "player 4" is no use to anybody
reading a lobby. CLIENT_HELLO carries a requested nickname now, and the server
decides what it actually is: trimmed of control characters and runs of spaces,
capped at 24, and made unique - two people called Marcin are two people and the
lobby has to say which is which. The result goes out as PEER_ROSTER whenever
somebody joins or leaves, and to a joining peer just before its snapshot, so the
crew section resolves to names rather than numbers. The name comes from
multiplayer.nickname in the ini or --nick on the command line, falling back to
the account name and, failing that, to the old numbering. The host is a peer
like any other here too, and registers its own name at startup.

Chat, on the key left of 1. Going up a line carries only its text: who said it
is decided by the connection it arrived on, never by the field in the packet,
which is what stops anybody putting words in anybody's mouth. The server tidies
and caps it, says it, and passes it on - a client waits to hear itself back, so
that everybody sees the conversation in the same order. While the box has the
keyboard imgui swallows the input before the driver mode sees it, so typing "d"
types "d" instead of opening the doors of whatever you are driving; that also
means the key that opened the panel cannot close it, hence escape.

And --nogui. No glfw, no window, no imgui, the null renderer, sound off, log to
the console it was started from, and nobody in a cab - the scenario is left to
its own drivers and this process is a referee rather than a participant. Every
window-dependent path is guarded on an empty window list rather than on a flag
scattered through the code, and the loop is paced at fifty steps a second
because nothing is waiting on a swapchain to slow it down. Chat lines go to the
log, which is what a machine with no window has instead of a chat panel.

    eu07.exe -s scenario.scn --host 0.0.0.0:7420 --nogui --nick Dispatcher

network/message.h

@@ -24,6 +24,8 @@ struct message
 		CLIENT_READY,
 		SNAPSHOT,
 		REQUEST_RESYNC,
+		PEER_ROSTER,
+		CHAT,
 		TYPE_MAX
 	};
 
@@ -49,6 +51,9 @@ struct client_hello : public message
 	// player who dropped out gets their seat and their peer id back. it is a reconnect
 	// token, not a credential - it says "this is the same session", nothing more
 	uint64_t session_token{ 0 };
+	// what the player would like to be called. a request, not a fact: the server tidies
+	// it up, makes it unique and hands back what it settled on
+	std::string nickname;
 };
 
 // sent by the server instead of SERVER_HELLO when the client cannot join;
@@ -140,6 +145,31 @@ struct request_resync : public message
 	virtual void deserialize(std::istream &stream) override;
 };
 
+// who is taking part, and what each of them is called. rebroadcast whenever somebody
+// joins or leaves, so that no peer has to guess at a name
+struct peer_roster : public message
+{
+	peer_roster() : message(PEER_ROSTER) {}
+
+	std::vector<peer_entry> peers;
+
+	virtual void serialize(std::ostream &stream) const override;
+	virtual void deserialize(std::istream &stream) override;
+};
+
+// something a participant said. going up it carries only the text - who said it is
+// decided by the connection it arrived on, never by what the sender put in the field
+struct chat_message : public message
+{
+	chat_message() : message(CHAT) {}
+
+	uint32_t peer{ PEER_NONE };
+	std::string text;
+
+	virtual void serialize(std::ostream &stream) const override;
+	virtual void deserialize(std::istream &stream) override;
+};
+
 // a peer asking the server to be put on the crew of a vehicle
 struct claim_vehicle : public message
 {