Sandy 3b,3z,4a

I modified 3b,3z and 4a.
The main changes include:
1) in 3b: add option for labelling duplicate on all rows or only on
rows with record_type == 0;
2) in 3z: add option for deleting duplicate or not ;
3) in 3z: split the dataset into tree datasets including train_pool,
train_target and customer_ID;
4) in 4a: keep some columns of the dataset and only implements handle
missing and normalisation on other columns of the dataset, and merge
these two parts together before return the dataset