add songs libraries (#490)

* first pass at adding song libraries

* start handling optional video

* fix song playback

* fix song transitions

* add songs page to UI

ErsatzTV.Core/Interfaces/Metadata/IFallbackMetadataProvider.cs

@@ -12,6 +12,7 @@ namespace ErsatzTV.Core.Interfaces.Metadata
         MovieMetadata GetFallbackMetadata(Movie movie);
         Option<MusicVideoMetadata> GetFallbackMetadata(MusicVideo musicVideo);
         Option<OtherVideoMetadata> GetFallbackMetadata(OtherVideo otherVideo);
+        Option<SongMetadata> GetFallbackMetadata(Song song);
         string GetSortTitle(string title);
     }
 }

ErsatzTV.Core/Interfaces/Metadata/ILocalMetadataProvider.cs

@@ -17,6 +17,7 @@ namespace ErsatzTV.Core.Interfaces.Metadata
         Task<bool> RefreshFallbackMetadata(Artist artist, string artistFolder);
         Task<bool> RefreshFallbackMetadata(MusicVideo musicVideo);
         Task<bool> RefreshFallbackMetadata(OtherVideo otherVideo);
+        Task<bool> RefreshFallbackMetadata(Song song);
         Task<bool> RefreshFallbackMetadata(Show televisionShow, string showFolder);
     }
 }

ErsatzTV.Core/Interfaces/Metadata/ISongFolderScanner.cs

@@ -0,0 +1,15 @@
+using System.Threading.Tasks;
+using ErsatzTV.Core.Domain;
+using LanguageExt;
+
+namespace ErsatzTV.Core.Interfaces.Metadata
+{
+    public interface ISongFolderScanner
+    {
+        Task<Either<BaseError, Unit>> ScanFolder(
+            LibraryPath libraryPath,
+            string ffprobePath,
+            decimal progressMin,
+            decimal progressMax);
+    }
+}

ErsatzTV.Core/Interfaces/Repositories/ISongRepository.cs

@@ -0,0 +1,17 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using ErsatzTV.Core.Domain;
+using ErsatzTV.Core.Metadata;
+using LanguageExt;
+
+namespace ErsatzTV.Core.Interfaces.Repositories
+{
+    public interface ISongRepository
+    {
+        Task<Either<BaseError, MediaItemScanResult<Song>>> GetOrAdd(LibraryPath libraryPath, string path);
+        Task<IEnumerable<string>> FindSongPaths(LibraryPath libraryPath);
+        Task<List<int>> DeleteByPath(LibraryPath libraryPath, string path);
+        Task<bool> AddTag(SongMetadata metadata, Tag tag);
+        Task<List<SongMetadata>> GetSongsForCards(List<int> ids);
+    }
+}