Advance test screens with button press.

[tinkeringjoe]

https://github.com/MakeMHz/xbox-hd-plus-app/blob/eb6a31ed19719d246bb392c1ea0907b890c26d48/source/scene1.cpp#L40

For display testing purposes it may be desired to stay on one of the test patterns for a longer period of time. Suggest using button press to advance through screens rather than a time based method.