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/engine.cpp

@@ -29,6 +29,7 @@
 #include "vehicle_func.h"
 #include "articulated_vehicles.h"
 #include "error.h"
+#include "engine_base.h"
 
 #include "table/strings.h"
 #include "table/engines.h"