Implemented the ability to allow the admin to change the cover generation size. (#2213)

Changed how covers are merged together. Now a cover image will always be generated for reading list and collections.

Fixed reading list page being a bit laggy due to a missing trackby function.

Reading list page will now show the cover image always. Collection detail page will only hide the image if there is no summary on the collection.

API/Entities/Enums/ServerSettingKey.cs

@@ -143,5 +143,10 @@ public enum ServerSettingKey
     /// </summary>
     [Description("OnDeckUpdateDays")]
     OnDeckUpdateDays = 26,
+    /// <summary>
+    /// The size of the cover image thumbnail. Defaults to <see cref="CoverImageSize"/>.Default
+    /// </summary>
+    [Description("CoverImageSize")]
+    CoverImageSize = 27
 
 }