Add XML docs to small session model types and remove CS1591 suppressions

MediaBrowser.Model/Session/MessageCommand.cs

@@ -1,17 +1,28 @@
 #nullable disable
-#pragma warning disable CS1591
 
 using System.ComponentModel.DataAnnotations;
 
 namespace MediaBrowser.Model.Session
 {
+    /// <summary>
+    /// A command to display a message on a client.
+    /// </summary>
     public class MessageCommand
     {
+        /// <summary>
+        /// Gets or sets the message header.
+        /// </summary>
         public string Header { get; set; }
 
+        /// <summary>
+        /// Gets or sets the message text.
+        /// </summary>
         [Required(AllowEmptyStrings = false)]
         public string Text { get; set; }
 
+        /// <summary>
+        /// Gets or sets the timeout in milliseconds after which the message should be dismissed.
+        /// </summary>
         public long? TimeoutMs { get; set; }
     }
 }