Release 6.20.0: Stabilized SOAP API

[changerequest]

The new implementation introduces a wrapper between the internal Java representation of the objects and the soap representation used by axis2 to generate the SOAP calls.

This keeps the SOAP API more stable, as potentially incompatible changes to the internal api are not automatically added to the soap API anymore.

This change does NOT introduce any changes to users using the API with perl or php.

However, users using the WSDL to generate code must regenerate the code!