Add admin action to regenerate QR codes

app/controllers/users_controller.rb

@@ -73,6 +73,15 @@ class UsersController < ApplicationController
     redirect_to users_path, notice: "Updated contestants: #{updated}/#{total}"
   end
 
+  def regenerate_qrcodes
+    authorize :user
+
+    Contestant.all.each do |contestant|
+      contestant.regenerate_qrcode
+      contestant.save
+    end
+  end
+
   private
 
   def set_user