Made the following additions:
Category: added recursive toString() /*hopefully it works*/ & amended
addChild() to include setting the parent, which meant adding the
addParent() method.
Company: added equals() code.
Item: filled in getQuantity() and getProduct(), unsure of
isNutritionalProduct() and toString().
NutritionalProduct: added initialization for some variables that I
missed (ie carb, protein & fat).
Product: added toString() & equals() code