[MLLIB] [SPARK-2222] Add multiclass evaluation metrics

Adding two classes: 
1) MulticlassMetrics implements various multiclass evaluation metrics
2) MulticlassMetricsSuite implements unit tests for MulticlassMetrics
Make a closure for this function and make the code align better.

~~~
... : Double = {
  val tp = tpByClass(label)
  val fp = fpByClass.getOrElse(label, 0)
  if (tp + fp == 0) 0 else tp.toDouble / (tp + fp)
}
~~~