Add support for tabs that cannot be selected

Introducing a TabItem.IsTabVisible property would be useful. 

Currently, if you want to hide a tab, you need to remove it from the TabView.Items collection and cache it in a backing collection.

Then, to re-show the tab, remove it from the cache and add it back to the TabItems (preferably at the same index if you've also cached it's position).

Add functionality to slide through the items like in a SlideView/Carousel.