+ added getter for CanteenSupply, setter for CanteenSupply
+ added getCashRegister() to apropiate lines
+ Created class CanteenSupply + added the methods
+ changed methods setAmountOfMoney and setAmountOfArticles to use a iterator + changed method checkout
+ Added method getTray
+ Added an Iterator to the class + Added a method to get the Iterator
+ Updated the lines where needed to use getCashRegister()
+ Added a test to test if you can get a tray using the getTray() Method
+ Updated the method testTray to use getTray() to get the tray
+ Added a test for the getArticleIterator() method in Tray.java