Improve payment error messages
Improve payment error messages

* Only show spinner after a few milliseconds, so immediate errors don't
  flash it

* Show Stripe errors in our normal .error element for better styling

* Remove unused code

Karspexet/Karspexet,Karspexet/Karspexet,Karspexet/Karspexet,Karspexet/Karspexet,Karspexet/Karspexet