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/landscape.cpp

@@ -31,6 +31,7 @@
 #include "pathfinder/npf/aystar.h"
 #include "saveload/saveload.h"
 #include "framerate_type.h"
+#include "landscape_cmd.h"
 #include <array>
 #include <list>
 #include <set>