Fix #630 -- manual check-in of attendees (#642)

* [WIP] manual check-in of attendees

This enables manual check-in of attendees.  The post-code was heavily
copied from the APIRedeemView of the pretixdroid, thus so far this seems
to be working, but I have a few questions:

The checkin-Objects generated by the pretixdroid-app have a nonce.
Should the checkin object generated here have a nonce, too?

Should the result of the check-in be noted in any other way than by the
change of the status?

* addressed review comments

* implement unit test for manual checkin

* fix style-issues

* Slight layout change

* Log who did the manual check-in

* Improve unit test to check the result of the action

src/tests/control/test_checkins.py

@@ -5,8 +5,8 @@ import pytest
 from django.utils.timezone import now
 
 from pretix.base.models import (
-    Checkin, Event, Item, ItemAddOn, ItemCategory, Order, OrderPosition,
-    Organizer, Team, User,
+    Checkin, Event, Item, ItemAddOn, ItemCategory, LogEntry, Order,
+    OrderPosition, Organizer, Team, User,
 )
 from pretix.control.views.dashboards import checkin_widget
 
@@ -269,6 +269,19 @@ def test_checkins_list_mixed(client, checkin_list_env, query, expected):
     assert item_keys == expected
 
 
+@pytest.mark.django_db
+def test_manual_checkins(client, checkin_list_env):
+    client.login(email='dummy@dummy.dummy', password='dummy')
+    assert not checkin_list_env[5][3].checkins.exists()
+    client.post('/control/event/dummy/dummy/checkins/', {
+        'checkin': [checkin_list_env[5][3].pk]
+    })
+    assert checkin_list_env[5][3].checkins.exists()
+    assert LogEntry.objects.filter(
+        action_type='pretix.control.views.checkin', object_id=checkin_list_env[5][3].order.pk
+    ).exists()
+
+
 @pytest.fixture
 def checkin_list_with_addon_env():
     # permission