Various fixes and improvements (#12878)

* Fix unused role routes being generated

* Remove unused JavaScript code

* Refactor filters code to be DRYer

* Fix `.count == 0` comparisons to `.empty?` in views

* Fix filters in views

config/routes.rb

@@ -231,7 +231,7 @@ Rails.application.routes.draw do
         end
       end
 
-      resource :role do
+      resource :role, only: [] do
         member do
           post :promote
           post :demote