Refactoring TrainVectorClassifier calls

Currently the OTB application for training models is launched using command line and system call.

It must use the python bindings.

The file train_vector.py contains the code which must be added to OtbAppBank.py

Several points must be done to use this:

• replace all occurrences
• change the configuration file to manipulate dictionary for classifier options like done for sampleSelection
• update configuration file conversion script to write the correct format for parameter ("arg_train", "options") -> remove it and create new parameter
• change the parameter type for ("arg_train", "options") in all concerned functions