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/Videos/VideoBanner.swift

@@ -219,22 +219,18 @@ struct VideoBanner: View {
         return watch!.finished ? 0.5 : 1
     }
 
-    private var thumbnailWidth: Double {
-        #if os(tvOS)
-            356
-        #else
-            120
-        #endif
-    }
-
     private var thumbnailHeight: Double {
         #if os(tvOS)
             200
         #else
-            72
+            75
         #endif
     }
 
+    private var thumbnailWidth: Double {
+        thumbnailHeight * Constants.aspectRatio16x9
+    }
+
     private var videoDurationLabel: String? {
         guard videoDuration != 0 else { return nil }
         return (videoDuration ?? video?.length)?.formattedAsPlaybackTime()