Minor changes I forgot to commit previously

NightScout/Alerters/RaspberryPiAudio.cs

@@ -0,0 +1,10 @@
+using System;
+namespace NightScout.Alerters
+{
+    public class EmptyClass
+    {
+        public EmptyClass()
+        {
+        }
+    }
+}

NightScout/Alerters/RaspberryPiAudioAlert.cs

@@ -46,6 +46,11 @@ namespace NightScout
             this.ButtonSource.ButtonStateChange += ButtonSource_ButtonStateChange;
         }
 
+        public void SetALSAAudioDevice(Int32 index)
+        {
+            this.PlayerCommandLine = String.Format("\"mpg123 -o alsa:hw:{0},0 ", index) + "-q {0}\"";
+        }
+
         private void ButtonSource_ButtonStateChange(bool obj)
         {
             Console.WriteLine("Button state change: {0}", obj);