Starting adaptation for CCD schematron use.

Starting to test using CCD schematron
Adding XSLT2 unit tests to reveal need for XmlPrime.
Starting migration from XDocument to XmlDocument.

In XRouter, SchemaTron was coded to the Xml.Linq.XDocument type. In
order to make use of XmlPrime for XSLT2/XPath2 support, it has to be
ported to leverage the System.Xml.XmlDocument type.