updating MediaController with AutoSelect option.

src/Umbraco.Core/Constants-Conventions.cs

@@ -122,6 +122,11 @@ namespace Umbraco.Core
 				/// MediaType alias for an image.
 				/// </summary>
 				public const string Image = "Image";
+
+                /// <summary>
+                /// MediaType alias indicating allowing auto-selection.
+                /// </summary>
+			    public const string AutoSelect = "umbracoAutoSelect";
 			}
             
 		    /// <summary>

src/Umbraco.Web/Editors/MediaController.cs

@@ -531,7 +531,7 @@ namespace Umbraco.Web.Editors
                 {
                     var mediaType = Constants.Conventions.MediaTypes.File;
 
-                    if (result.FormData["contentTypeAlias"] == Constants.Conventions.MediaTypes.Image)
+                    if (result.FormData["contentTypeAlias"] == Constants.Conventions.MediaTypes.AutoSelect)
                     {
                         if (UmbracoConfig.For.UmbracoSettings().Content.ImageFileTypes.Contains(ext))
                         {