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_client.cpp

@@ -1000,11 +1000,7 @@ NetworkRecvStatus ClientNetworkGameSocketHandler::Receive_SERVER_CHAT(Packet *p)
 				ci = NetworkClientInfo::GetByClientID(_network_own_client_id);
 				break;
 
-			/* For speaking to company or giving money, we need the company-name */
-			case NETWORK_ACTION_GIVE_MONEY:
-				if (!Company::IsValidID(ci_to->client_playas)) return NETWORK_RECV_STATUS_OKAY;
-				FALLTHROUGH;
-
+			/* For speaking to company, we need the company-name */
 			case NETWORK_ACTION_CHAT_COMPANY: {
 				StringID str = Company::IsValidID(ci_to->client_playas) ? STR_COMPANY_NAME : STR_NETWORK_SPECTATORS;
 				SetDParam(0, ci_to->client_playas);