Cover Image Picking + Forwarding Headers with EPUBs (#700)

* Ensure Kavita knows about forwarding headers (fixes issue with epub urls not going through https with reverse proxy). Fixed a case where cover image selection preferred nested folders vs files in root directory.

* Fixed broken unit test

* Added bug that I fixed to the unit tests

API/Startup.cs

@@ -138,7 +138,10 @@ namespace API
 
             app.UseResponseCompression();
 
-            app.UseForwardedHeaders();
+            app.UseForwardedHeaders(new ForwardedHeadersOptions
+            {
+                ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto
+            });
 
             app.UseRouting();