update default image providers

MediaBrowser.Controller/Providers/ImageRefreshMode.cs

@@ -0,0 +1,25 @@
+namespace MediaBrowser.Controller.Providers
+{
+    public enum ImageRefreshMode
+    {
+        /// <summary>
+        /// The none
+        /// </summary>
+        None = 0,
+
+        /// <summary>
+        /// The default
+        /// </summary>
+        Default = 1,
+
+        /// <summary>
+        /// Existing images will be validated
+        /// </summary>
+        ValidationOnly = 2,
+
+        /// <summary>
+        /// All providers will be executed to search for new metadata
+        /// </summary>
+        FullRefresh = 3
+    }
+}