use blurhash for song backgrounds (#526)

* generate blurhash for all local artwork

* use blurhash song background if available

* only write blur hash to disk once

* use multiple blur hashes

* update changelog

* fix song detail outline

* reset song metadata (artwork)

ErsatzTV.Core/Interfaces/FFmpeg/IFFmpegProcessService.cs

@@ -50,7 +50,7 @@ namespace ErsatzTV.Core.Interfaces.FFmpeg
             MediaVersion videoVersion,
             string videoPath,
             bool boxBlur,
-            Option<int> randomColor,
+            Option<string> watermarkPath,
             ChannelWatermarkLocation watermarkLocation,
             int horizontalMarginPercent,
             int verticalMarginPercent,

ErsatzTV.Core/Interfaces/Images/IImageCache.cs

@@ -1,6 +1,7 @@
 using System.IO;
 using System.Threading.Tasks;
 using ErsatzTV.Core.Domain;
+using ErsatzTV.Core.Interfaces.FFmpeg;
 using LanguageExt;
 
 namespace ErsatzTV.Core.Interfaces.Images
@@ -12,5 +13,7 @@ namespace ErsatzTV.Core.Interfaces.Images
         Task<Either<BaseError, string>> CopyArtworkToCache(string path, ArtworkKind artworkKind);
         string GetPathForImage(string fileName, ArtworkKind artworkKind, Option<int> maybeMaxHeight);
         Task<bool> IsAnimated(string fileName);
+        Task<string> CalculateBlurHash(string fileName, ArtworkKind artworkKind, int x, int y);
+        Task<string> WriteBlurHash(string blurHash, IDisplaySize targetSize);
     }
 }