pep8 blank lines fixes

flake8 --select W391,E302,E301,E304

autopep8 can't fix W391 even though it claims it can.
Fixed using a simple custom script.

weboob/core/ouiboube.py

@@ -111,6 +111,7 @@ class WebNip(object):
         :param backend_name: name of backend we can't load
         :param exception: exception object
         """
+
         def __init__(self, backend_name, exception):
             Exception.__init__(self, unicode(exception))
             self.backend_name = backend_name