support plot keywords

MediaBrowser.Controller/Entities/IHasKeywords.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace MediaBrowser.Controller.Entities
+{
+    public interface IHasKeywords
+    {
+        /// <summary>
+        /// Gets or sets the keywords.
+        /// </summary>
+        /// <value>The keywords.</value>
+        List<string> Keywords { get; set; }
+    }
+
+    public static class KeywordExtensions
+    {
+        public static void AddKeyword(this IHasKeywords item, string name)
+        {
+            if (string.IsNullOrWhiteSpace(name))
+            {
+                throw new ArgumentNullException("name");
+            }
+
+            if (!item.Keywords.Contains(name, StringComparer.OrdinalIgnoreCase))
+            {
+                item.Keywords.Add(name);
+            }
+        }
+    }
+}