废弃 huey，多数据库连接的时候存在 connection 无法释放的问题，回到 celery

oj/__init__.py

@@ -7,3 +7,8 @@
                                                         |___/                |___/      |_|
 https://github.com/QingdaoU/OnlineJudge
 """
+from __future__ import absolute_import
+
+# This will make sure the app is always imported when
+# Django starts so that shared_task will use this app.
+from .celery import app as celery_app