Fix inconsistent value of numTrees in DetectorCascade and EnsembleClassifier

 In current version, it seems that the default value of `numTrees` and `numFeatures` initialized in `DetectorCascade` is opposite to `EnsembleClassifier`. Though the former will be propagated to the latter,  `numTrees` is still regarded as 10 (hard-coded) when used to update the classifier. 

This PR is trying to fix it. If I misunderstand the code, please excuse me and tell me the truth.