Improved thumbnail handling

- ThumbnailsModel optionally returns the quality
- Have constants for 4:3 and 16:9 aspect ratio
- Add high quality options for thumbnails
- Rename Highest quality to Best quality
- make 4:3 thumbnails fill the VideoCell
- use .maxes instead of .maxresdefault (the latter sometimes returns white images)

Signed-off-by: Toni Förster <toni.foerster@gmail.com>

Shared/Player/Video Details/ChapterView.swift

@@ -65,7 +65,7 @@ import SwiftUI
         }
 
         static var thumbnailHeight: Double {
-            thumbnailWidth / (16 / 9)
+            thumbnailWidth / Constants.aspectRatio16x9
         }
     }
 
@@ -119,7 +119,7 @@ import SwiftUI
         }
 
         static var thumbnailHeight: Double {
-            thumbnailWidth / 1.7777
+            thumbnailWidth / Constants.aspectRatio16x9
         }
     }
 #endif