Use config setting to decide if web content should be hosted

Also fail server startup if web content is expected but missing

MediaBrowser.Controller/IServerApplicationHost.cs

@@ -16,11 +16,6 @@ namespace MediaBrowser.Controller
     {
         event EventHandler HasUpdateAvailableChanged;
 
-        /// <summary>
-        /// Gets a value indicating whether the server is hosting the static web content from jellyfin-web.
-        /// </summary>
-        bool IsHostingContent { get; }
-
         /// <summary>
         /// Gets the system info.
         /// </summary>