Use logger instead of prints

[guilyx]

import logging
logging.basicConfig(filename='app.log', encoding='utf-8', level=logging.DEBUG)
logging.debug('This message should go to the log file')
logging.info('So should this')
logging.warning('And this, too')
logging.error('And non-ASCII stuff, too, like Øresund and Malmö')

• Add app.log to gitignore
• Replace info prints by logging.info
• Replace non critical failures by logging.debug (ex: when no path is found)
• Add error logging on critical failures (not sure yet if there should be any)