fix(ionReorderButton): stop `ngRepeat:dupes` error when reordering

Closes #1601.

BREAKING CHANGE: Reordering with ion-reorder-button no longer changes the order of the items in the DOM.

This change will only break your list if you were not using the
onReorder callback as described in the documentation.

Before, while reordering an element in a list Ionic would swap the
elements underneath as the reordering happened.  This sometimes caused
errors with angular's ngRepeat directive.

Now, reordering an element in a list does not change the order of
elements in the DOM.  It is expected that the end developer will use the
index changes given in the `onReorder` callback to reorder the items
in the list. This is simple to do, see the [examples in the
ionReorderButton
documentation](http://ionicframework.com/docs/api/directive/ionReorderButton/).