MRG: synchronize remote-tracking branch 'remotes/origin/develop' into unsupervised_classif

Conflicts:
      Modules/Applications/AppClassification/app/otbTrainImagesClassifier.cxx
      Modules/Applications/AppClassification/app/otbTrainVectorClassifier.cxx
      Modules/Learning/LearningBase/include/otbImageClassificationFilter.h
      Modules/Learning/LearningBase/include/otbImageClassificationFilter.txx
      Modules/Learning/LearningBase/include/otbMachineLearningModel.h
      Modules/Learning/LearningBase/include/otbMachineLearningModel.txx
      Modules/Learning/LearningBase/include/otbMachineLearningModelFactoryBase.h
      Modules/Learning/LearningBase/include/otbSharkUtils.h