[Feature] Create StateTrigger for SignedIn State

## Describe the problem this feature would solve
Would be great to have [StateTrigger](https://docs.microsoft.com/en-us/uwp/api/windows.ui.xaml.statetrigger) and/or some other XAML helpers for the current state of authentication (loading, signed-in, signed-out) so that controls or other UI could be shown/hidden easily.