InvoiceTest fixed to match changes
Customer menu completed in ShopNoGUI
Merge branch 'master' into Shane
Order and Sale tests updated to work with changes to Order and Sale.
Stock test also update. Phone number added to Supplier
Merged master into darren
Changed sale and order classes to have their own stock and product
lists.
Product has optional quantity.
Stock change
Change Stock
Appended Stock class
	Added/ updated methods:
	checkStock()
	processSale()
	checkSellBy()
	stockLevels()
Appended Supplier class
	Added checkPrice() method