Params search works with nested hostgroups

This tiny tiny PR allows you to search (UI or API) on parameters that are inherited from hostgroups. 

For instance, imagine a host 'foo.cern.ch', and a hostgroup 'bar/baz'. If hostgroup 'bar' defines a parameter 'firewall = on', 'foo.cern.ch' will inherit it. Nonetheless, if you use the search bar, and search for 'params.firewall = true', it will not show 'foo.cern.ch' unless you move it to '/bar/' instead of '/bar/baz'