Polish noun templates - tantum parameter

I had the same idea for the longest time (except I named the argument |num=)… but I never really got around to implement it.

Anyway, it works now for {{pl-decl-noun-ja}}. If someone moves the rest of the specialised declension patterns into Module:pl-noun (and switches templates to use that module), they shall start supporting it too.

Seems to work, with the exception that [[category:Polish singularia tantum]] is not added.

Fixed.