pagination: avoid counting pages outside searches.

Replace this common pattern in controllers:

    @tags = Tag.search(search_params).paginate(params[:page], :limit => params[:limit], :search_count => params[:search])

with this:

    @tags = Tag.paginated_search(params)

`search_count` is used to skip doing a full page count when we're not
doing a search (on the assumption that the number of results will be
high when not constrained by a search). We didn't do this consistently
though. Refactor to do this in every controller.

app/models/application_record.rb

@@ -6,6 +6,11 @@ class ApplicationRecord < ActiveRecord::Base
       def paginate(*options)
         extending(PaginationExtension).paginate(*options)
       end
+
+      def paginated_search(params)
+        search_params = params.fetch(:search, {}).permit!
+        search(search_params).paginate(params[:page], limit: params[:limit], search_count: params[:search])
+      end
     end
   end