Harden XML parsing via Apache Commons Secure XML

[beth-soptim]

https://github.com/apache/commons-secure-xml

WSS4J recently also switched to Apache Commons Secure XML: apache/ws-wss4j#673

[phax]

Well, I am not 100% convinced this is a good solution.
As I already solved the issue with secure XML parsing in ph-commons this would just introduce a new dependency that would need maintenance.
Instead I would make sure, that the same hardening of components is applied in ph-commons...