Improve logging

[integraledelebesgue]

Issue

The custom Logger isn't valuable in the current form.

We need the following functionalities:

• A notion of log level, with the possibility to set via CLI
• Saving logs to file

Additional ideas requiring further specification:

• Design a context manager that emits logs on enter and exit (it can measure execution time too...). Invoke whole procedures inside this context (or a null context, depending on a flag)
• Implement specialized logging callbacks for models (e.g. visitors) which will analyze the returned results and inform about errors/Nones