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

modules/opensimplex/noise_texture.h

@@ -33,8 +33,8 @@
 
 #include "open_simplex_noise.h"
 
-#include "core/image.h"
-#include "core/reference.h"
+#include "core/io/image.h"
+#include "core/object/reference.h"
 #include "editor/editor_node.h"
 #include "editor/editor_plugin.h"
 #include "editor/property_editor.h"