custom collection playback order (#64)

* add custom index to collection items

* add custom collection order to ui

* cleanup

ErsatzTV.Core/Domain/Collection/Collection.cs

@@ -6,6 +6,7 @@ namespace ErsatzTV.Core.Domain
     {
         public int Id { get; set; }
         public string Name { get; set; }
+        public bool UseCustomPlaybackOrder { get; set; }
         public List<MediaItem> MediaItems { get; set; }
         public List<CollectionItem> CollectionItems { get; set; }
     }

ErsatzTV.Core/Domain/Collection/CollectionItem.cs

@@ -6,5 +6,6 @@
         public Collection Collection { get; set; }
         public int MediaItemId { get; set; }
         public MediaItem MediaItem { get; set; }
+        public int? CustomIndex { get; set; }
     }
 }