Fix bug #56814 - Switch from dom4j to JAXP

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1617428 13f79535-47bb-0310-9956-ffa450edef68
Add some extra safety test to check that external entities are not loaded by xmlbeans

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1617453 13f79535-47bb-0310-9956-ffa450edef68
sync merge to trunk

git-svn-id: https://svn.apache.org/repos/asf/poi/branches/xml_signature@1617624 13f79535-47bb-0310-9956-ffa450edef68
sync test

git-svn-id: https://svn.apache.org/repos/asf/poi/branches/xml_signature@1617627 13f79535-47bb-0310-9956-ffa450edef68