Add BlurHash support to backend

MediaBrowser.Controller/Drawing/IImageProcessor.cs

@@ -32,6 +32,13 @@ namespace MediaBrowser.Controller.Drawing
         /// <returns>ImageDimensions</returns>
         ImageDimensions GetImageDimensions(string path);
 
+        /// <summary>
+        /// Gets the blurhash of the image.
+        /// </summary>
+        /// <param name="path">Path to the image file.</param>
+        /// <returns>BlurHash</returns>
+        String GetImageHash(string path);
+
         /// <summary>
         /// Gets the dimensions of the image.
         /// </summary>