[UPDATE] SoapHeader improvements

After one case that breaks, we discover one little bug when catching
data for SoapHeaders from schemas. Indeed, the namespace was wrong and
the name of the parameter too. We made sure data are retrieved from the
right WSDL attributes and that each SoapHeader is well defined in the
Service class.

Put setSoapHeader method in the *WsdlClass so each Service class can
call it which simplifies its definition