SPARK-4156 [MLLIB] EM algorithm for GMMs

Implementation of Expectation-Maximization for Gaussian Mixture Models.

This is my maiden contribution to Apache Spark, so I apologize now if I have done anything incorrectly; having said that, this work is my own, and I offer it to the project under the project's open source license.


This does not work; the compiler can not find a suitable implicit conversion for the array of vectors when attempting x.sum