Add XML docs to small entity interfaces and remove CS1591 suppressions

MediaBrowser.Controller/Entities/IHasStartDate.cs

@@ -1,11 +1,15 @@
-#pragma warning disable CS1591
-
 using System;
 
 namespace MediaBrowser.Controller.Entities
 {
+    /// <summary>
+    /// Interface for items that have a start date.
+    /// </summary>
     public interface IHasStartDate
     {
+        /// <summary>
+        /// Gets or sets the start date.
+        /// </summary>
         DateTime StartDate { get; set; }
     }
 }