Set logger in struphy __init__.py

[spossann]

This PR goes into use-logging-instead-of-print, see #199

I read that the logger should be set up at the beginning of the entry point of the program. Since we do not have a clear entry point, the best thing is to maybe setup in the struphy __init__.py.

• move logger setup to struphy __init__.py
• do not use .json file to avoid importing struphy for the path
• use function set_logger_level to set the level of all handlers

The function set_logger_level can be tested with python src/struphy/utils/utils.py.

I set the default level to logging.WARNING.