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/tree_cmd.cpp

@@ -23,6 +23,7 @@
 #include "core/random_func.hpp"
 #include "newgrf_generic.h"
 #include "date_func.h"
+#include "tree_cmd.h"
 
 #include "table/strings.h"
 #include "table/tree_land.h"