When you just update/replace the widget there is no need for an animation
to occur. Thus why animations where broken before. This commit is not ideal
as it makes it the responsibility of the caller to declare valid(UX wise)
transitions.
This commit reimplements support for the empty view in the ShowStack.
The current structure is the following:
* A Content stack which holds the HomeStack and the ShowStack.
It's what is used in the headerbar StackSwitcher.
* The HomeStack is composed of the HomeView and an EmptyView.
* The ShowStack is composed of the PopulatedStack and an EmptyView.
* The PopulatedStack is composed of the ShowsView and the ShowWidget
currently. An AboutEpisode widget is planned to be added here also.
