[SPARK-17139][ML] Add model summary for MultinomialLogisticRegression

## What changes were proposed in this pull request?

Add 4 traits, using the following hierarchy:
LogisticRegressionSummary
LogisticRegressionTrainingSummary: LogisticRegressionSummary
BinaryLogisticRegressionSummary: LogisticRegressionSummary
BinaryLogisticRegressionTrainingSummary: LogisticRegressionTrainingSummary, BinaryLogisticRegressionSummary

and the public method such as `def summary` only return trait type listed above.

and then implement 4 concrete classes:
LogisticRegressionSummaryImpl (multiclass case)
LogisticRegressionTrainingSummaryImpl (multiclass case)
BinaryLogisticRegressionSummaryImpl (binary case).
BinaryLogisticRegressionTrainingSummaryImpl (binary case).

## How was this patch tested?

Existing tests & added tests.

Author: WeichenXu <[email protected]>

Closes apache#15435 from WeichenXu123/mlor_summary.

Author: WeichenXu123