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/mono/editor/code_completion.h

@@ -31,8 +31,8 @@
 #ifndef CODE_COMPLETION_H
 #define CODE_COMPLETION_H
 
-#include "core/ustring.h"
-#include "core/variant.h"
+#include "core/string/ustring.h"
+#include "core/variant/variant.h"
 
 namespace gdmono {