[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 change the method to `fMeasure(label: Double)` and `fMeasure(label: Double, beta: Double)`? The former computes F1 while the latter computes F_beta.

`={` -> `= {`