Use @conference for current_conference if available

This means the top menu would work on the conferences#show page.

app/controllers/management/management_controller.rb

@@ -12,9 +12,13 @@ module Management
     helper_method :current_conference?
 
     def current_conference
-      if not @current_conference and params[:conference_id].present?
+      if not @current_conference
+        if @conference
+          @current_conference = @conference
+        elsif params[:conference_id].present?
           @current_conference = Conference.find(params[:conference_id])
         end
+      end
 
       @current_conference
     end