Refactor Devise integration

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

app/controllers/registrar/profile_controller.rb

@@ -5,13 +5,13 @@ class Registrar
     helper_method :linked_users
 
     def show
-      @user = current_user
+      @user = current_registrar_user
     end
 
     private
 
     def linked_users
-      current_user.linked_users
+      current_registrar_user.linked_users
     end
   end
 end