feat: Completely rework notification framework

This change is needed as
a) there are many different types of notifications. A notification about a new comment does not only relate the comment but also adoption notice and a user that made the comment. Therefore, I introduce a new general notification that has optional links to other objects.
b) this change allows to define a different representation of e-mails vs. display on the website. The new notification type is in charge of representation from now on. Title and text will be deprecated and eventually removed

src/fellchensammlung/tools/search.py

@@ -3,7 +3,8 @@ from django.utils.translation import gettext_lazy as _
 
 from .geo import LocationProxy, Position
 from ..forms import AdoptionNoticeSearchForm
-from ..models import SearchSubscription, AdoptionNotice, AdoptionNoticeNotification, SexChoicesWithAll, Location
+from ..models import SearchSubscription, AdoptionNotice, SexChoicesWithAll, Location, \
+    Notification, NotificationTypeChoices
 
 
 def notify_search_subscribers(adoption_notice: AdoptionNotice, only_if_active: bool = True):
@@ -20,10 +21,11 @@ def notify_search_subscribers(adoption_notice: AdoptionNotice, only_if_active: b
         search = Search(search_subscription=search_subscription)
         if search.adoption_notice_fits_search(adoption_notice):
             notification_text = f"{_('Zu deiner Suche')} {search_subscription} wurde eine neue Vermittlung gefunden"
-            AdoptionNoticeNotification.objects.create(user=search_subscription.owner,
-                                                      title=f"{_('Neue Vermittlung')}: {adoption_notice}",
-                                                      adoption_notice=adoption_notice,
-                                                      text=notification_text)
+            Notification.objects.create(user_to_notify=search_subscription.owner,
+                                        notification_type=NotificationTypeChoices.AN_FOR_SEARCH_FOUND,
+                                        title=f"{_('Neue Vermittlung')}: {adoption_notice}",
+                                        adoption_notice=adoption_notice,
+                                        text=notification_text)
             logging.debug(f"Notification for search subscription {search_subscription} was sent.")
         else:
             logging.debug(f"Adoption notice {adoption_notice} was not fitting the search subscription.")