Check that client is playing the right item

Send date when playback command is emitted
Rename some classes

MediaBrowser.Model/Syncplay/GroupUpdate.cs

@@ -0,0 +1,26 @@
+namespace MediaBrowser.Model.Syncplay
+{
+    /// <summary>
+    /// Class GroupUpdate.
+    /// </summary>
+    public class GroupUpdate<T>
+    {
+        /// <summary>
+        /// Gets or sets the group identifier.
+        /// </summary>
+        /// <value>The group identifier.</value>
+        public string GroupId { get; set; }
+
+        /// <summary>
+        /// Gets or sets the update type.
+        /// </summary>
+        /// <value>The update type.</value>
+        public GroupUpdateType Type { get; set; }
+
+        /// <summary>
+        /// Gets or sets the data.
+        /// </summary>
+        /// <value>The data.</value>
+        public T Data { get; set; }
+    }
+}