Ignore whitespace when reading serialized XML objects.

This was previously effectively being done by XmlDocument in the multiple passes through the XML.
This change tells XmlReader to ignore whitespace.  This also means changing arguments to use XmlReader instead of XmlTextReader (a descendent of XmlReader) directly.
XmlReader.Create() has been the recommend way to create XML readers since .NET 2.0 as per MS SDK and is the only way to specific ignore whitespace settings.