Partial fix for using scale2x, hq2x algorithms

* Game.cpp: Remove setting default log level for
NOM_CATEGORY_APPLICATION; this is already done for us within nomlib.
Update code to latest API in nomlib's feature/GUI dev branch

* Remove calls to SpriteBatch::update; this is now handled
internally, and thus has been put under protected scope.
Update code to latest API in nomlib's feature/GUI dev branch

* Rename UIEvent to GUIEvent; this was a conflict with
nom::UIEvent.
Refactored audio subsystem (it is now an optional component)