Reorganized core/ directory, it was too fatty already

-Removed FuncRef, since Callable makes it obsolete
-Removed int_types.h as its obsolete in c++11+
-Changed color names code

scene/2d/path_2d.cpp

@@ -30,7 +30,7 @@
 
 #include "path_2d.h"
 
-#include "core/engine.h"
+#include "core/config/engine.h"
 #include "core/math/geometry_2d.h"
 #include "scene/scene_string_names.h"