Indexing pricing items by name

Indexing with database IDs made it harder later to validate the input against the structure returned by PriceCalculatorImpl::fetchPricing().
Passing form values on validation redirect
Beetter styling and original price displayed
Correcting help text placement
Discount code form validation
Reset validation status on unchecking item
Code form inside a panel
Button usability fixes

Replacing label on button to a more precise statement when the email checkbox is checked.