Add confusion matrix metrics

[feifjiang]

Added confusion matrix for multi-class classification, including:

• confusion matrix for the topK most occurring labels
• the topN predictions/labels for each label/prediction category

[salesforce-cla[bot]]

Thanks for the contribution! Unfortunately we can't verify the commit author(s): FeiFei Jiang f***@f***.i***.s***.com. One possible solution is to add that email to your GitHub account. Alternatively you can change your commits to another email and force push the change. After getting your commits associated with your GitHub account, sign the Salesforce.com Contributor License Agreement and this Pull Request will be revalidated.

[codecov[bot]]

Codecov Report

Merging #530 (fd24753) into master (13ad9cd) will increase coverage by 86.77%. The diff coverage is 95.23%.

@@             Coverage Diff             @@
##           master     #530       +/-   ##
===========================================
+ Coverage        0   86.77%   +86.77%     
===========================================
  Files           0      347      +347     
  Lines           0    12018    +12018     
  Branches        0      621      +621     
===========================================
+ Hits            0    10429    +10429     
- Misses          0     1589     +1589     

Impacted Files	Coverage Δ
...op/evaluators/OpMultiClassificationEvaluator.scala	95.59% <95.23%> (ø)
...a/com/salesforce/op/test/FeatureTypeEquality.scala	80.00% <0.00%> (ø)
.../op/stages/impl/feature/SubstringTransformer.scala	100.00% <0.00%> (ø)
...scala/com/salesforce/op/stages/MetadataParam.scala	66.66% <0.00%> (ø)
...op/stages/impl/feature/TimePeriodTransformer.scala	100.00% <0.00%> (ø)
...ala/com/salesforce/op/utils/tuples/RichTuple.scala	100.00% <0.00%> (ø)
.../op/stages/impl/feature/TextMapNullEstimator.scala	100.00% <0.00%> (ø)
...op/stages/impl/selector/ModelSelectorSummary.scala	91.83% <0.00%> (ø)
.../ml/dmlc/xgboost4j/scala/spark/XGBoostParams.scala	95.00% <0.00%> (ø)
...src/main/scala/com/salesforce/op/cli/gen/Ops.scala	94.00% <0.00%> (ø)
... and 338 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 13ad9cd...fd24753. Read the comment docs.