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_cmd.cpp

@@ -26,6 +26,7 @@
 #include "company_base.h"
 #include "order_backup.h"
 #include "cheat_type.h"
+#include "order_cmd.h"
 
 #include "table/strings.h"