Allow collection sort by Release Date Descending

- default sort is still Release Date Ascending
- choosing sort by Release Date will change it to sort by Release Date Descending

This is because most people go to collections to browse new movies to watch, and recently released movies should be on top.

MediaBrowser.Controller/Entities/Movies/BoxSet.cs

@@ -125,7 +125,7 @@ namespace MediaBrowser.Controller.Entities.Movies
             if (string.Equals(DisplayOrder, "PremiereDate", StringComparison.OrdinalIgnoreCase))
             {
                 // Sort by release date
-                return LibraryManager.Sort(children, user, new[] { ItemSortBy.ProductionYear, ItemSortBy.PremiereDate, ItemSortBy.SortName }, SortOrder.Ascending).ToList();
+                return LibraryManager.Sort(children, user, new[] { ItemSortBy.ProductionYear, ItemSortBy.PremiereDate, ItemSortBy.SortName }, SortOrder.Descending).ToList();
             }
 
             // Default sorting