Codechange: Let the compile generate the master command table out of templated command traits.

This is using a non-intrusive type-traits like templated system, which
allows compile-time validation that the command table and the command
enum match up.

src/order_backup.cpp

@@ -16,6 +16,7 @@
 #include "vehicle_base.h"
 #include "window_func.h"
 #include "station_map.h"
+#include "order_cmd.h"
 
 #include "safeguards.h"