Fix #571 -- Partial payments and refunds

src/pretix/plugins/paypal/migrations/0002_referencedpaypalobject_payment.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.13 on 2018-07-23 09:19
+from __future__ import unicode_literals
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0097_auto_20180722_0804'),
+        ('paypal', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='referencedpaypalobject',
+            name='payment',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, to='pretixbase.OrderPayment'),
+        ),
+    ]