[CXF-5527] Update the SAAJStreamWriter to use the SAAJ methods to create children of Body and Header so that they end up as the proper SOAPHeaderElement or SOAPBodyElement types immediately.  Otherwise, they may be converted to those types later.

git-svn-id: https://svn.apache.org/repos/asf/cxf/trunk@1561774 13f79535-47bb-0310-9956-ffa450edef68