Overhaul usage of logging

[okin]

Is your feature request related to a problem? Please describe.
Most classes have log_level as their first param.
The class should not control how it's messages are logged.

Describe the solution you'd like
I'd expect the logging to be configured when running one of the scripts from CLI.
Classes should not require a log_level parameter.

Describe alternatives you've considered
I think using the standard logging system is without good alternatives.
I would like to keep it but have it restructured.

Additional context
Python's logging cookbook has some good insights into how to set up your loggers.