Price update for attribute selection

The module adds a new price field "Your choice".

When you click on an attribute, the display is updated and the total price appears that would be due if you clicked on "buy" now.

Risks and side effects: does not work with graduated prices and does not work if customers have Javascript turned off in their browser.

Additional work possible: including fallback to normal attribute selection when visiting without Javascript or via mobile phone;
including adaptation to your template.