Return `label_cls` or guess one from the first element of `labels`.

def get_label_cls(self, labels, label_cls:Callable=None, label_delim:str=None, **kwargs):
        "Return `label_cls` or guess one from the first element of `labels`."
        if label_cls is not None:               return label_cls
        if self.label_cls is not None:          return self.label_cls
        if label_delim is not None:             return MultiCategoryList
        it = index_row(labels,0)
        if isinstance(it, (float, np.float32)): return FloatList
        if isinstance(try_int(it), (str, Integral)):  return CategoryList
        if isinstance(it, Collection):          return MultiCategoryList
        return ItemList