Enlarge search and sort to refinements

Hi,

When searching by field with the advanced form, searches are strictly limited to their field and refinements are not used, although they are defined in the plugin. So this patch adds an option to allow to enlarge searches to refinements. For example, a search on the field `Dublin Core : Rights` will search on this element, but on the fields `Dublin Core : Access Rights` and `Dublin Core : License` too.

Sincerely,

Daniel Berthereau
Infodoc & Knowledge management