update database connection
enw BoghtItemTest Class
add calculate_price_test
update calculate_price_test
update calculatePrice Method and calculate_price test
udpate Promotion Class
update PrintItem VO
update BoughtItem and BoughtItemList
add calculate Method to BoughtItem
change BuyTwoGetOneFreePromotion to extends Promotion Class
change DiscountPromotion to extends Promotion Class
change SecondHalfPricePromotion Promotion to extends Promotion Class
update Promotion Class
update PromotionType and DisonutPromotion
udpate
new BoughtItemService Class
new BoughtItemServiceTest Class
move calucate_price_test to BoughtItemServiceTest
update  test
fix BuyTwoGetOntFree Test