Changed win logic

[jaydenwindle]

Fixes:

• Added a winners list to the giveaway model so we can persist the list of winners
• Added item_won to user model to store the product id if the user wins
• Changed show route to list participants if giveaway is still ongoing, otherwise list all the winners and the things they won
• Disabled the ajax participant count update in dash_main.js because it was running too often and causing shopify to reject subsequent API calls