Refactor Devise integration

- Use scoped users
- Use the named route helpers instead of hardcoded paths

app/controllers/admin/base_controller.rb

@@ -1,10 +1,20 @@
 module Admin
   class BaseController < ApplicationController
-    before_action :authenticate_user!
+    before_action :authenticate_admin_user!
     helper_method :head_title_sufix
 
     def head_title_sufix
       t(:admin_head_title_sufix)
     end
+
+    private
+
+    def current_ability
+      @current_ability ||= Ability.new(current_admin_user)
+    end
+
+    def user_for_paper_trail
+      current_admin_user.present? ? current_admin_user.id_role_username : 'public'
+    end
   end
-end
+end