Fix #297 -- pretixdroid: Show metrics in the control panel (#481)

* add checkin status page

add dashboard widget
add checkin page under orders

* modify checkin logic

added new fields in checkin page
added filter items

* add tests for checkins & minor improvement

* support addin_product & noadm setting logic

* remove name ordering check test case

src/pretix/control/views/dashboards.py

@@ -168,6 +168,27 @@ def shop_state_widget(sender, **kwargs):
     }]
 
 
+@receiver(signal=event_dashboard_widgets)
+def checkin_widget(sender, **kwargs):
+    size_qs = OrderPosition.objects.filter(order__event=sender, order__status='p')
+    checked_qs = OrderPosition.objects.filter(order__event=sender, order__status='p', checkins__isnull=False)
+
+    # if this setting is False, we check only items for admission
+    if not sender.settings.ticket_download_nonadm:
+        size_qs = size_qs.filter(item__admission=True)
+        checked_qs = checked_qs.filter(item__admission=True)
+
+    return [{
+        'content': NUM_WIDGET.format(num='{}/{}'.format(checked_qs.count(), size_qs.count()), text=_('Checked in')),
+        'display_size': 'small',
+        'priority': 50,
+        'url': reverse('control:event.orders.checkins', kwargs={
+            'event': sender.slug,
+            'organizer': sender.organizer.slug
+        })
+    }]
+
+
 @receiver(signal=event_dashboard_widgets)
 def welcome_wizard_widget(sender, **kwargs):
     template = get_template('pretixcontrol/event/dashboard_widget_welcome.html')