CGE2: Some more minor cleanup
CGE2: Some repair in Bitmap::code().
CGE2: Rework the handling of the sound buttons on the toolbar.

Also keep in sync the volume settings and the audio mode of the game and the settings in the Launcher.
CGE2: Properly fade out if the player exits during the intro too.
CGE2: Rework canSaveGameStateCurrently().
CGE2: Get rid of _keyAlt.