core: resync widgets only when they are visible: using AUTO_RESYNC from QuickApp was causing performance trouble (resynchronising all widgets was freezing the frontend for a little while). By resynchronising only when the widget is visible, this should be greatly improved.

[DEFAULT]
bridge = pb
log_level = debug
log_fmt = #[%%(levelname)s][%%(name)s] %%(message)s

[cagou]
log_level = debug
log_fmt = [%%(levelname)s][%%(name)s] %%(message)s