Added HTML-to-XML PDI step plugin

This PDI step plugin uses JTidy to parse HTML and convert it to well-formed XML or XHTML for processing by other PDI steps such as Get Data from XML.  It was inspired by Roland Bouman's blog post using the UDJC step and JTidy (http://rpbouman.blogspot.com/2011/05/using-tidy-to-clean-webpages-with.html)