Don't cherry-pick

Don't cherry-pick
- added entity for registering bonus cards, they will connect the buyer's "contact"
  entity with receipt entity
- added field for whether the item is a discount
- added field for item's coupon number
- removed percentage/fixed discounts as this should be done with fake products
- removed unique constrain between item's product and receipt as same discounts
  may be applied on more than one item

Signed-off-by: Roland Häder <roland@mxchange.org>