[Web-Request] Use rich header (closes #2204164) Unify header management. All web request use the Headers class now (imported from twisted). Code dedicated to header management have been merged into the base WebRequest class.

# -*- 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 specific hooks and operations"""