Incorrect level of xerces and xml-api packaged in webapp samples

A number of webapp samples contain xerces 2.6.2 and xml-apis-1.0.b2, causing NoSuchMethodError and VerifyError exceptions on WebSphere 6.1 for example. This will probably happen as well on other Web containers, even though it doesn't seem to cause a problem on Tomcat.

These old Jars are dragged in by axiom-api for example. Exclusions should be added to the Tuscany pom.xml files that reference axiom-api, like binding-ws-axis2 already does. Dependencies on xerces 2.8.1 should be added and the contribution module which uses xml-api should reference xml-api 1.3.03.