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

Adding two classes: 
1) MulticlassMetrics implements various multiclass evaluation metrics
2) MulticlassMetricsSuite implements unit tests for MulticlassMetrics
Could you make this one take an optional beta parameter as well? Maybe change the name to `weightedFMeasure` and implement both `weightedFMeasure()` and `weightedFMeasure(beta)`?