//Concrete class from abstract class ListItem & use in a linked list class to implement a linked list that will
//add items in order(sorted alphabetically)
//duplicated items not added
//rules for adding item:
//if the head of list is null - head refer to item to be added
//if item to be added is less than current item in list - add item before current(make previous item refer to this)
//if item is greater than current - move onto next item and compare again(if not next item - that's where it goes)
//also need a remove method(remove from list)