prepare vrt file in background thread.

app/jobs/views.py

@@ -24,7 +24,8 @@ def delete_job(job_id):
     if not (job.creator == current_user or current_user.is_administrator()):
         abort(403)
     delete_thread = threading.Thread(target=background_delete_job,
-                                     args=(current_app, job_id))
+                                     args=(current_app._get_current_object(),
+                                           job_id))
     delete_thread.start()
     flash('Job has been deleted!')
     return redirect(url_for('main.dashboard'))