stages/invitation: start extracting invitation from core

passbook/core/migrations/0014_delete_invitation.py

@@ -0,0 +1,14 @@
+# Generated by Django 3.0.5 on 2020-05-11 19:57
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("passbook_core", "0013_delete_debugpolicy"),
+    ]
+
+    operations = [
+        migrations.DeleteModel(name="Invitation",),
+    ]