OPDS-PS v1.2 Support + a few bugfixes (#1869)

* Fixed up a localization lookup test case

* Refactored some webp to a unified method

* Cleaned up some code

* Expanded webp conversion for covers to all entities

* Code cleanup

* Prompt the user when they are about to delete multiple series via bulk actions

* Aligned Kavita to OPDS-PS 1.2.

* Fixed a bug where clearing metadata filter of series name didn't clear the actual field.

* Added some documentation

* Refactored how covert covers to webp works. Now we will handle all custom covers for all entities. Volumes and Series will not be touched but instead be updated via a RefreshCovers call. This will fix up the references much faster.

* Fixed up the OPDS-PS 1.2 attributes to only show on PS links

API/Services/ImageService.cs

@@ -125,6 +125,11 @@ public class ImageService : IImageService
         return Task.FromResult(outputFile);
     }
 
+    /// <summary>
+    /// Performs I/O to determine if the file is a valid Image
+    /// </summary>
+    /// <param name="filePath"></param>
+    /// <returns></returns>
     public async Task<bool> IsImage(string filePath)
     {
         try