WebSearch: faceted results order fix

• Quickly fixes order of faceted search results. (addresses #1352)

• Improves speed of loading websearch blueprint by moving facet plugins discovery to before_first_app_request handler.

• TODO improve perform_request_search to return intbitset with results and eventually raise exception when nothing is found with near search terms.

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>