support external subtitles (#745)

* support external subtitles in local movie libraries

* code cleanup

* simplify subtitle updating

* skip external subtitles from media servers

* fix plex subtitles

ErsatzTV.Core.Tests/Fakes/FakeLocalFileSystem.cs

@@ -45,6 +45,10 @@ public class FakeLocalFileSystem : ILocalFileSystem
     public IEnumerable<string> ListFiles(string folder) =>
         _files.Map(f => f.Path).Filter(f => Path.GetDirectoryName(f) == folder);
 
+    // TODO: this isn't accurate, need to use search pattern
+    public IEnumerable<string> ListFiles(string folder, string searchPattern) =>
+        _files.Map(f => f.Path).Filter(f => Path.GetDirectoryName(f) == folder);
+
     public bool FileExists(string path) => _files.Any(f => f.Path == path);
     public bool FolderExists(string folder) => false;
 

ErsatzTV.Core.Tests/Fakes/FakeTelevisionRepository.cs

@@ -67,7 +67,9 @@ public class FakeTelevisionRepository : ITelevisionRepository
     public Task<Either<BaseError, PlexSeason>> GetOrAddPlexSeason(PlexLibrary library, PlexSeason item) =>
         throw new NotSupportedException();
 
-    public Task<Either<BaseError, PlexEpisode>> GetOrAddPlexEpisode(PlexLibrary library, PlexEpisode item) =>
+    public Task<Either<BaseError, MediaItemScanResult<PlexEpisode>>> GetOrAddPlexEpisode(
+        PlexLibrary library,
+        PlexEpisode item) =>
         throw new NotSupportedException();
 
     public Task<bool> AddGenre(ShowMetadata metadata, Genre genre) => throw new NotSupportedException();