Inset an Axiom element to the current message. The target to insert the OMElement can be
1. A property
2. SOAP Body child element
3. SOAP envelope
4. A XPath expression to get the correct node
In case the target is an SOAP Envelope, the current SOAP envelope will be replaced by the
OMNode. So the OMNode must me a SOAPEnvelope.
In case of Body the first child of the Body will be replaced by the new Node or a sibling
will be added to it depending on the replace property.
In case of Expression a SOAP Element will be chosen based on the XPath. If replace is true
that element will be replaced, otherwise a sibling will be added to that element.
Property case is simple. The OMNode will be stored in the given property