move apps to own dir

apps/activity/apps.py

@@ -0,0 +1,11 @@
+# -*- mode: python; coding: utf-8 -*-
+# Copyright (C) 2018-2019 by BDE ENS Paris-Saclay
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from django.apps import AppConfig
+from django.utils.translation import gettext_lazy as _
+
+
+class ActivityConfig(AppConfig):
+    name = 'activity'
+    verbose_name = _('activity')