add the ability to reload 'YTDL_OPTIONS' when file is modified

ui/src/app/downloads.service.ts

@@ -39,6 +39,7 @@ export class DownloadsService {
   queueChanged = new Subject();
   doneChanged = new Subject();
   customDirsChanged = new Subject();
+  ytdlOptionsChanged = new Subject();
   configurationChanged = new Subject();
   updated = new Subject();
 
@@ -98,6 +99,10 @@ export class DownloadsService {
       this.customDirs = data;
       this.customDirsChanged.next(data);
     });
+    socket.fromEvent('ytdl_options_changed').subscribe((strdata: string) => {
+      let data = JSON.parse(strdata);
+      this.ytdlOptionsChanged.next(data);
+    });
   }
 
   handleHTTPError(error: HttpErrorResponse) {