Added base classes to encapsulate metadata in media

Aurora/Backend/Models/Media/BaseMetadata.cs

@@ -0,0 +1,17 @@
+using System;
+namespace Aurora.Backend.Models.Media
+{
+    public class BaseMetadata
+    {
+        public BaseMetadata()
+        {
+        }
+
+        /// <summary>
+        /// Extra data associated with a song.
+        /// </summary>
+        /// <value></value>
+        public object ExtraData { get; set; }
+
+    }
+}