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)
The HTML pattern is too broad; it matches plain text. Every HTML pattern should have at least a `<` in it, e.g. `<[^>]+/binaries/(?:[^/]+/)*content/gallery/`. Please also use non-capturing groups (`(?:)` instead of `()`) unless to groups are used for version detection.