Use ion-item in collection repeat demo

On slide 30, demonstrating complex lists, you make use of ion-item. Then on slide 31 showing collection-repeat, you revert back to a div with a class. This works of course, but I think it is better to be consistent and use the directive version. Plus it is pretty impressive to point out how you can go from a 'normal' list to a better performing one with one tiny edit.
