7.0: fix flake8 errors

Fix flake8 errors to get a clean build:

* mostly line wrapping / reindenting
* in super_calendar, extracted a method from an already too large method to gain 2 indentation levels and some clarity
* added local copy of images for super_calendar documentation

On my way, fixed a couple of calls to logging.logger methods which did the param substitutions using % rather than delegating this to the logging handler. 

AFAIK parenthesis is useless here (already inside parenthesis)