Auto-check-in for specific sales channels (#1409)

* Autocheckin data model/cosmetics

* Expose automatically checked-in OrderPositions

* Expose automatically checked-in OrderPositions in CSV/PDF Exports

* Fix some tests, try to fix MultiStringField/CheckboxSelectMultiple

* Actually fix MultiStringField/CheckboxSelectMultiple.
(Not pretty, but it works)

* Fix more tests

* Squash migration

* Also fix CSV/nameparts-test

* Changes for Autocheckin code-review

* Perform Auto-Checkins through new core plugin

* Update config-doc to reflect also checkinlists

* Explicitly output AutoCheckin Yes/No for CSV-Export (+ fix test)

* Move autocheckin from plugin to service

* API-doc

* Fix API-doc spelling

* Checkinlist-API and autocheckin order tests

* Performance improvement when reading checkinlists for autocheckin

Co-Authored-By: Raphael Michel <michel@rami.io>

* Autocheckin test for order created through API

* Resolve migration conflict

src/pretix/base/migrations/0136_auto_20190918_1742.py

@@ -0,0 +1,25 @@
+# Generated by Django 2.2 on 2019-09-18 17:42
+
+from django.db import migrations, models
+
+import pretix.base.models.fields
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0135_auto_20191007_0803'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='checkin',
+            name='auto_checked_in',
+            field=models.BooleanField(default=False),
+        ),
+        migrations.AddField(
+            model_name='checkinlist',
+            name='auto_checkin_sales_channels',
+            field=pretix.base.models.fields.MultiStringField(default=[]),
+        )
+    ]