core: handle URLs opening in a per-platform way: URLs opening may have to be done in a different way according to platforms, so an `open_url` method has been created in base Platform which can be overriden.

[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