Remove preprocessing config from loading functions

Summary

This MR introduces the following changes

• Removing the preprocessing config from the load functions and replace it with the scale dict, the only thing that is needed from the config.
• get_test_sample and get_test_sample_trks can now take the path of the var_dict and the scale_dict or directly the loaded dicts
• Adding possibility to define which step of evaluate_model.py is run via command line argument.
• Removing useless tagger command line option from evaluate_model.py. This is a needed variable in the train config and therefore always given.
• Adding progress bar to the different steps of the evaluate_model.py script. By default, this is False. When calling evaluate_model.py with -v, the progress bar is shown.

Conformity

• Changelog entry
• Documentation
• Development guidelines
• Style guides