Add PDA Ringtones (#5842)

Co-authored-by: metalgearsloth <comedian_vs_clown@hotmail.com>

Content.Shared/PDA/Ringer/RingerVisuals.cs

@@ -0,0 +1,12 @@
+using System;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.PDA.Ringer
+{
+    [Serializable, NetSerializable]
+    public enum RingerUiKey
+    {
+        Key
+    }
+
+}