[server] Implement CGameMode ctor/dtor

* Add CGameMode::Unload stub

server/gamemodes.cpp

@@ -0,0 +1,18 @@
+
+#include "main.h"
+
+CGameMode::CGameMode()
+{
+	field_68 = 0;
+	field_69 = 0;
+}
+
+CGameMode::~CGameMode()
+{
+	Unload();
+}
+
+void CGameMode::Unload()
+{
+	// TODO: CGameMode::Unload() W .text:0046D7B0 L .text:080A4DB0
+}