Added a way to change the loss function used during training

MLP/include/MLP.hpp

MLP/src/MLP.cpp

error_correction/src/macaon_train_error_detector.cpp

maca_common/include/ProgramParameters.hpp

maca_common/src/ProgramParameters.cpp

trainer/src/macaon_train.cpp

transition_machine/include/Classifier.hpp

transition_machine/src/Classifier.cpp