KMeans support instance weighting

Since https://issues.apache.org/jira/browse/SPARK-9610, we start to support instance weighting in ML.

However, Clustering and other impl in features still do not support instance weighting.

I think we need to start support weighting in KMeans, like what scikit-learn does.

It will contains three parts:

1, move the impl from .mllib to .ml

2, make .mllib.KMeans as a wrapper of .ml.KMeans

3, support instance weighting in the .ml.KMeans