add music artist channel folder type

MediaBrowser.Model/Channels/ChannelFolderType.cs

@@ -6,6 +6,8 @@ namespace MediaBrowser.Model.Channels
 
         MusicAlbum = 1,
 
-        PhotoAlbum = 2
+        PhotoAlbum = 2,
+
+        MusicArtist = 3
     }
 }

MediaBrowser.Server.Implementations/Channels/ChannelManager.cs

@@ -1250,6 +1250,10 @@ namespace MediaBrowser.Server.Implementations.Channels
                 {
                     item = GetItemById<MusicAlbum>(info.Id, channelProvider.Name, channelProvider.DataVersion, out isNew);
                 }
+                else if (info.FolderType == ChannelFolderType.MusicArtist)
+                {
+                    item = GetItemById<MusicArtist>(info.Id, channelProvider.Name, channelProvider.DataVersion, out isNew);
+                }
                 else if (info.FolderType == ChannelFolderType.PhotoAlbum)
                 {
                     item = GetItemById<PhotoAlbum>(info.Id, channelProvider.Name, channelProvider.DataVersion, out isNew);