cagou widget: don't add header_input systematically anymore: header input is often used in CagouWidget for e.g. filtering, but not always, and when it is not, it is weird and confusing to have a TextInput which doesn't do nothing. To avoid that, a new `use_header_input` bool attribute (set to False by default) has been added to CagouWidget.

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

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