ENH: Add Neural Network machine learning model.

...ilitiesAdapters/OpenCV/otbMachineLearningModelFactory.txx

...iesAdapters/OpenCV/otbNeuralNetworkMachineLearningModel.h

...sAdapters/OpenCV/otbNeuralNetworkMachineLearningModel.txx

...ters/OpenCV/otbNeuralNetworkMachineLearningModelFactory.h

...rs/OpenCV/otbNeuralNetworkMachineLearningModelFactory.txx

Testing/Code/Learning/CMakeLists.txt

Testing/Code/Learning/otbLearningTests6.cxx

Testing/Code/Learning/otbMachineLearningModelCanRead.cxx

Testing/Code/Learning/otbTrainMachineLearningModel.cxx