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

editor/groups_editor.h

@@ -31,7 +31,7 @@
 #ifndef GROUPS_EDITOR_H
 #define GROUPS_EDITOR_H
 
-#include "core/undo_redo.h"
+#include "core/object/undo_redo.h"
 #include "editor/scene_tree_editor.h"
 #include "scene/gui/button.h"
 #include "scene/gui/dialogs.h"