title: Spree - count discount on product show page
body: <p>Is there a way in spree to calculate discount for product, based on promotions, and show it on product show page? Currently, i know that it is possible to show all adjustments on order page, but I would like to show possible price for every product while user is browsing products. Also, I would like to show taxes that are going to be applied to product.</p>
  
  <p>Thanks!</p>