Validation against schemas during parsing added

The built in schemas the generated files was created from was added to
project as a consequence of this.
Faults in test xmls discovered and fixed because of this. Elements were
removed from where they were not allowed.
Extra filler objects created in some of the tests, so that the objects
passed to parser comply with schemas.
A severe bug in XPath evaluation of topics was discovered and fixed. The
automatically generated TopicSet was not schema compliant, but now is.