uc_donation_incentives 6.x-1.0

Initial commit. Ubercart Donation Incentives allows a store owner to apply donation incentives to products. These incentives can be thought of as rebates on the purchase, with the rebate being a donation amount. The donation incentives can either be a fixed amount, or a percentage of the sell price. A default donation incentive can be applied to all products, and can also be set on a per-product basis.