Show announcements in timetable views

Blocked by AlekSIS!184 (merged)

Closes #63 (closed)

aleksis/apps/chronos/models.py

@@ -8,6 +8,7 @@ from django.core import validators
 from django.core.exceptions import ValidationError
 from django.db import models
 from django.db.models import F, Max, Min, Q
+from django.db.models.aggregates import Count
 from django.db.models.functions import Coalesce
 from django.forms import Media
 from django.http.request import QueryDict