UI loading improvements

Fixed: Caching for dynamically loaded JS files
Fixed: Incorrect caching of initialize.js
(cherry picked from commit f0cb5b81f140c67fa84162e094cc4e0f3476f5da)

src/Radarr.Http/Frontend/Mappers/HtmlMapperBase.cs

@@ -62,9 +62,11 @@ namespace Radarr.Http.Frontend.Mappers
                     url = cacheBreakProvider.AddCacheBreakerToPath(match.Groups["path"].Value);
                 }
 
-                return string.Format("{0}=\"{1}{2}\"", match.Groups["attribute"].Value, UrlBase, url);
+                return $"{match.Groups["attribute"].Value}=\"{UrlBase}{url}\"";
             });
 
+            text = text.Replace("__URL_BASE__", UrlBase);
+
             _generatedContent = text;
 
             return _generatedContent;