Fix models ForeignKeys, move search index to core

aleksis/apps/chronos/models.py

@@ -550,7 +550,7 @@ class LessonPeriod(WeekAnnotationMixin, TeacherPropertiesMixin, ExtensibleModel)
         else:
             return self.lesson.teachers
 
-    def get_room(self) -> Optional[core.Room]:
+    def get_room(self) -> Optional[Room]:
         if self.get_substitution() and self.get_substitution().room:
             return self.get_substitution().room
         else:

aleksis/apps/chronos/search_indexes.py

-from aleksis.core.models import Room
-from aleksis.core.util.search import Indexable, SearchIndex
-
-
-class RoomIndex(SearchIndex, Indexable):
-    """Haystack index for searching rooms."""
-
-    model = Room

aleksis/apps/chronos/views.py

@@ -7,7 +7,7 @@ from django.http import HttpRequest, HttpResponse, HttpResponseNotFound
 from django.shortcuts import get_object_or_404, redirect, render
 from django.urls import reverse
 from django.utils import timezone
-from django.utils.translation import ugettext as _
+from django.utils.translation import gettext as _
 from django.views.decorators.cache import never_cache
 
 import reversion