merge C&C and RA music player logic

mainly code cleanup, but with the following improvements:
- scroll to current song which fixes #3360 and overlapping label
- use Rules.InstalledMusic & Sound.MusicPlaying everywhere
- separated C&C install logic and log catched exceptions
- save the music settings on back/close

OpenRA.Game/GameRules/Settings.cs

@@ -100,9 +100,11 @@ namespace OpenRA.GameRules
 		public float SoundVolume = 0.5f;
 		public float MusicVolume = 0.5f;
 		public float VideoVolume = 0.5f;
+
 		public bool Shuffle = false;
 		public bool Repeat = false;
 		public bool MapMusic = true;
+
 		public string Engine = "AL";
 		public string Device = null;