Make recurring period a database model

- For easier handling (foreignkeys, many2many)
- For higher flexibility (users can define their own periods)

uncloud_pay/migrations/0027_auto_20201006_1319.py

@@ -0,0 +1,41 @@
+# Generated by Django 3.1 on 2020-10-06 13:19
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('uncloud_pay', '0026_order_should_be_billed'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='RecurringPeriod',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=100, unique=True)),
+                ('duration_seconds', models.IntegerField(unique=True)),
+            ],
+        ),
+        migrations.DeleteModel(
+            name='SampleOneTimeProduct',
+        ),
+        migrations.DeleteModel(
+            name='SampleRecurringProduct',
+        ),
+        migrations.DeleteModel(
+            name='SampleRecurringProductOneTimeFee',
+        ),
+        migrations.AlterField(
+            model_name='order',
+            name='recurring_period',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='uncloud_pay.recurringperiod'),
+        ),
+        migrations.AlterField(
+            model_name='product',
+            name='default_recurring_period',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='uncloud_pay.recurringperiod'),
+        ),
+    ]