Add rendering for tourism=wilderness_hut

[vibrog]

For cabins used by wilderness/mountain hikers, there is a type with facilities between the staffed tourism=alpine_hut and amenity=shelter. Here in Norway, these are used to represent cabins operated by the Norwegian hiking association and other similar organisations. We see map contributors change these cabins to tourism=alpine_hut because tourism=wilderness_hut is not rendered, which make them appear on the map as staffed tourist cabins.

See http://wiki.openstreetmap.org/wiki/Tag:tourism=wilderness_hut

[matkoniecz]

duplicate of #540