added playlist loader

registered appconfig as singleton
added config interfaces

Tv7Playlist.Core/IPlaylistLoader.cs

@@ -0,0 +1,11 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Tv7Playlist.Core.Parsers;
+
+namespace Tv7Playlist.Core
+{
+    public interface IPlaylistLoader
+    {
+        Task<IReadOnlyCollection<ParsedTrack>> LoadPlaylistFromUrl();
+    }
+}