Encapsulate discretization in Event::discretize_timeslots

Encapsulates the code to select the timeslot discretization.

Addresses #15 (closed)

AKModel/models.py

@@ -383,7 +383,7 @@ class Event(models.Model):
             )
 
     def discretize_timeslots(self, *, slots_in_an_hour: float = 1.0) -> Iterable[TimeslotBlock]:
-        if DefaultSlot.objects.filter(event=self.event).exists():
+        if DefaultSlot.objects.filter(event=self).exists():
             # discretize default slots if they exists
             yield from merge_blocks(self.default_time_slots(slots_in_an_hour=SLOTS_IN_AN_HOUR))
         else: