Display a timeline on the dashboard (#1290)

* Timeline data model

* Display timeline

* …

* More events

* Plugin support

* Fix docs typo

src/tests/base/test_timeline.py

@@ -0,0 +1,50 @@
+from datetime import datetime
+from decimal import Decimal
+
+import pytest
+import pytz
+
+from pretix.base.models import Event, Organizer
+from pretix.base.timeline import timeline_for_event
+
+tz = pytz.timezone('Europe/Berlin')
+
+
+def one(iterable):
+    found = False
+    for it in iterable:
+        if it:
+            if found:
+                return False
+            else:
+                found = True
+    return found
+
+
+@pytest.fixture
+def event():
+    o = Organizer.objects.create(name='Dummy', slug='dummy')
+    event = Event.objects.create(
+        organizer=o, name='Dummy', slug='dummy',
+        date_from=datetime(2017, 10, 22, 12, 0, 0, tzinfo=tz),
+        date_to=datetime(2017, 10, 23, 23, 0, 0, tzinfo=tz),
+    )
+    return event
+
+
+@pytest.fixture
+def item(event):
+    return event.items.create(name='Ticket', default_price=Decimal('23.00'))
+
+
+@pytest.mark.django_db
+def test_event_dates(event):
+    tl = timeline_for_event(event)
+    assert one([
+        e for e in tl
+        if e.event == event and e.datetime == event.date_from and e.description == 'Your event starts'
+    ])
+    assert one([
+        e for e in tl
+        if e.event == event and e.datetime == event.date_to and e.description == 'Your event ends'
+    ])