findMissingProducts() implemented
findMissingProducts() changed to private
Implemented putInShoppingCart() and takeProductsFromBuyZone()
Implemented step() and fixed findMissingProducts()
Changed Product price to BigDecimal
Merge pull request #9 from remynaps/price

Changed Product price to BigDecimal
Expanded step() to go to next buyzone
Moved logic to goToNextBuyZone()
Merge pull request #10 from remynaps/gotobuyzone

Gotobuyzone
Implemented goToCashRegister
Refactored step().
Refactored code a little
Added some discount stuffs
Merged disc into develop