Simplified the usage of the fade over screen.
Better performance.
BUGFIX: dispose the current screen if the game is disposed.
BUGFIX: check for the assetmanager being null before calling methods on it.
BUGFIX: don't stop() music in dispose
Added 'directFLush' flag to MuteManager and TrialUtil. Then found out that Gdx.app.getPreferences() returns a new object on every call and that settings were not stored in the object that got flushed in pause() and dispose(). Finally added BureauGame.bootGame() so a preferences object could be created that is valid for the whole app life cycle.
The engine now manages a global preferences instance.
On Android, Preferences must be flushed before an updated value can be read. Since we now only flush on pause/exit, the Player objects need to be reused. Positive side effects: less memory allocation.