Use yaml

[vict0rsch]

Mainly:

• Use YAML not json as it is more versatile, human-readable and commentable
  • we can still use shortcut json-like notations for lists ([]) and dicts ({})
• Run Black formatter on some locations
• Create a data field in the conf along with train and model so code in train.py is updated
• Refactor some code
  • putting code from train.py to utils.py
  • more pythonic gitignore
  • safer loading of overriding confs when running experiments

[vict0rsch]

This merge will implement breaking changes from existing configuration files ; they just need to be translated from json to yaml and then everything will work as before but now we can use comments