[SPARK-5895] [ML] Add VectorSlicer - updated

Add VectorSlicer transformer to spark.ml, with features specified as either indices or names.  Transfers feature attributes for selected features.

Updated version of [https://github.com/apache/spark/pull/5731]

CC: yinxusen This updates your PR.  You'll still be the primary author of this PR.

CC: mengxr

Author: Xusen Yin <yinxusen@gmail.com>
Author: Joseph K. Bradley <joseph@databricks.com>

Closes #7972 from jkbradley/yinxusen-SPARK-5895 and squashes the following commits:

b16e86e [Joseph K. Bradley] fixed scala style
71c65d2 [Joseph K. Bradley] fix import order
86e9739 [Joseph K. Bradley] cleanups per code review
9d8d6f1 [Joseph K. Bradley] style fix
83bc2e9 [Joseph K. Bradley] Updated VectorSlicer
98c6939 [Xusen Yin] fix style error
ecbf2d3 [Xusen Yin] change interfaces and params
f6be302 [Xusen Yin] Merge branch 'master' into SPARK-5895
e4781f2 [Xusen Yin] fix commit error
fd154d7 [Xusen Yin] add test suite of vector slicer
17171f8 [Xusen Yin] fix slicer
9ab9747 [Xusen Yin] add vector slicer
aa5a0bf [Xusen Yin] add vector slicer