Add New Sampling Algorithm for Each Sampling

[zhangpengshan]

In Shifu, only Random#nextDouble algorithm are used. Check if any kind of other sampling algorithm can be used.

Check sampling algorithm, what is down sampling and how down sampling can be used in Shifu, how to make sure distributions is the same before and after sampling.

[zhangpengshan]

Using PossonSampler for baggingWithReplacement sampling

[zhangpengshan]

Think about how to replace Random#nextDouble

[zhangpengshan]

In spark Random#nextDouble is also used while there are some optimization if threshold is two small.

It's ok for us as it is not our bottleneck so far.