Friesian add_hist_seq and add_neg_hist_seq unsupport string

[yizerozhuang]

When using the add_neg_hist_seq and add_hist_seq method in Friesian, it only allows list of int in the columns, it doesn't allow list of string in the column. So string to index must be done before this step. It would be nice to support string as well.

[hkvision]

This might be combined with intel-analytics/BigDL#5053