scanning and poster improvements (#24)

* first pass at refresh-all-metadata by source

* add version to startup logs

* lock media source during refresh

* fix local media source "name" in collection editor

* optimize scanning so playouts only rebuild when necessary

* support more poster file types

* more scanning improvements; check for missing posters during scans

ErsatzTV.Application/MediaSources/Commands/ScanLocalMediaSource.cs

@@ -1,9 +1,11 @@
 using ErsatzTV.Core;
+using ErsatzTV.Core.Metadata;
 using LanguageExt;
 using MediatR;
 
 namespace ErsatzTV.Application.MediaSources.Commands
 {
-    public record ScanLocalMediaSource(int MediaSourceId) : IRequest<Either<BaseError, string>>,
+    public record ScanLocalMediaSource(int MediaSourceId, ScanningMode ScanningMode) :
+        IRequest<Either<BaseError, string>>,
         IBackgroundServiceRequest;
 }