Use a choice field for invoice address countries

src/pretix/base/migrations/0070_auto_20170719_0910.py

@@ -0,0 +1,43 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.2 on 2017-07-19 09:10
+from __future__ import unicode_literals
+
+import django_countries
+from django.db import migrations, models
+
+
+def fwd(app, schema_editor):
+    InvoiceAddress = app.get_model('pretixbase', 'InvoiceAddress')
+    for ia in InvoiceAddress.objects.all():
+        if ia.company or ia.vat_id:
+            ia.is_business = True
+            ia.save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0069_invoice_prefix'),
+    ]
+
+    operations = [
+        migrations.RenameField(
+            model_name='invoiceaddress',
+            old_name='country',
+            new_name='country_old',
+        ),
+        migrations.AddField(
+            model_name='invoiceaddress',
+            name='country',
+            field=django_countries.fields.CountryField(default='', max_length=2, verbose_name='Country'),
+            preserve_default=False,
+        ),
+        migrations.AddField(
+            model_name='invoiceaddress',
+            name='is_business',
+            field=models.BooleanField(default=False, verbose_name='Business customer'),
+        ),
+        migrations.RunPython(
+            fwd, migrations.RunPython.noop
+        ),
+    ]