Simplified App Open and init*()

[johsoe]

Due to a recent discovery in that MaterialApp.router() exposes a builder: method where the BuildContext has initialised Localizations etc, we can put in NStack there and "go back" to the simpler approach.

We also wrap our internal NStackScope widget in a FutureBuilder that awaits minor state loading, such as overwritten locale or other stuff further down the line.