[web] Avoid using an empty dict as default parameter of 'CubicWebRequestBase'.
Also update the related docstring of the __init__ method.
# -*- coding: utf-8 -*-
# copyright %(year)s %(author)s, all rights reserved.
# contact %(author-web-site)s -- mailto:%(author-email)s
#
%(long-license)s
"""%(distname)s views/forms/actions/components for web ui"""