fix: hide checkout details and payment container during processing

This commit hides the elements '.quiqqer-simple-checkout-orderDetails' and '.quiqqer-simple-checkout__scrollToPaymentContainer' in 'SimpleCheckout.js' during processing. When the element with '.quiqqer-order-step-processing' class is present, the mentioned elements are set to 'display: none', preventing them from being viewed during order processing. The same logic applies when the order is successful, ensuring a cleaner interface during these steps.

Related: #22 (closed)