add ability to have non-expiring nonces, clean up expired nonces

passbook/core/migrations/0022_nonce_expiring.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.1.7 on 2019-04-04 19:42
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('passbook_core', '0021_policy_timeout'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='nonce',
+            name='expiring',
+            field=models.BooleanField(default=True),
+        ),
+    ]