add package model
move cartitem to model
move product to model
rename promotionHelper to promotionService
move promotionService to service package
rename DataProvider to ProductService
move productService to service package
rename fileHelper to FileUtils
add fileUtils to utils package
add DbUtils
add getConnection method
add close method
add test PromotionFactoryTest
modify getInstance method
modify Promotion
rename promotion to PromotionFactory
add category.java
modify product.java