Category in Special:SearchByProperty causes an empty entry

Forwarding a category to Special:SearchByProperty via Special:Browse causes an empty content because the internal category Id '_INST' isn't resolved.

This change forwards a category/sub-category to an appropriate Special:Browse link.

### Category: vs Category::
Before this change `[[Category:Prop1]]` `[[Category::Prop2]]` would create two different entities a "Category" and a "Property" which from a semantic declaration point of view doesn't make much sense as both represents the same "Category" entity.

With this PR either notion (`[[Category:Prop1]]`, `[[Category::Prop2]]`) will point to the "Category" entity and is always resolved as '_INST'.