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/mono_gd/support/android_support.h

@@ -33,7 +33,7 @@
 
 #if defined(ANDROID_ENABLED)
 
-#include "core/ustring.h"
+#include "core/string/ustring.h"
 
 namespace gdmono {
 namespace android {