Added detection for Hippo

This is a detection for Hippo CMS. This open source cms is used by several sites of the Dutch government.
Some sites that should be detectable are:
- www.defensie.nl (Ministry of Defense)
- www.uva.nl (University of Amsterdam)
- www.ns.nl (Dutch railroads)
thanks for your response. I was a bit aware of the broadness, but your solution is much better. Problem was that I saw different situations, for example "<div ns:background="/binaries/content/gallery/zonetaxi_980x460.jpg" >"