MusicPlayer: add Enabled bool (defaults to off)

Shared/MusicPlayer.cs

@@ -4,6 +4,8 @@ using System;
 namespace SemiColinGames {
   public class MusicPlayer : IDisposable {
 
+    public static bool Enabled = false;
+
     private SoundEffectInstance music;
 
     ~MusicPlayer() {
@@ -34,7 +36,9 @@ namespace SemiColinGames {
     }
 
     public void Play() {
+      if (Enabled) {
         music?.Play();
       }
     }
   }
+}