Extract response element name into a method

I'm writing to a standard that has Name{Request,Response} as the request and response element names, so putting this logic in a method lets me subclass SoapDispatcher and change this behavior.
Update helpers.py

Adding headers support for httplib2 request
Update client.py

Adding support for headers in client when WSDL is behind Basic Auth
Add CDATA support

Tested with `python -m unittest tests.simplexmlelement_test`
Merge pull request #10 from tanderson3/master

Adding Headers support for WSDL access with Basic Auth
Merge pull request #9 from tkho/element_name

Extract response element name into a method
Merge pull request #11 from tkho/cdata

Add CDATA support
removed test of AFIP webservice no longer available
fixed url in mexican webservice e-invoice test