Change: move "give money" from client-list to company window

This is a much better location for this button, as you send
money from one company to another company, not from player
to player.

This is based on work done by JGRPP in:
f820543391
and surrounding commits, which took the work from estys:
https://www.tt-forums.net/viewtopic.php?p=1183311#p1183311

We did modify it to fix several bugs and clean up the code while
here anyway.

The callback was removed, as it meant a modified client could
prevent anyone from seeing money was transfered. The message
is now generated in the command itself, making that impossible.

src/network/network_server.cpp

@@ -1382,9 +1382,6 @@ NetworkRecvStatus ServerNetworkGameSocketHandler::Receive_CLIENT_CHAT(Packet *p)
 
 	NetworkClientInfo *ci = this->GetInfo();
 	switch (action) {
-		case NETWORK_ACTION_GIVE_MONEY:
-			if (!Company::IsValidID(ci->client_playas)) break;
-			FALLTHROUGH;
 		case NETWORK_ACTION_CHAT:
 		case NETWORK_ACTION_CHAT_CLIENT:
 		case NETWORK_ACTION_CHAT_COMPANY: