Use logging module

[pierrepo]

Some ressources:

• https://gist.github.com/ibeex/3257877
• https://stackoverflow.com/questions/14037975/how-do-i-write-flasks-excellent-debug-log-message-to-a-file-in-production
• https://fangpenlin.com/posts/2012/08/26/good-logging-practice-in-python/