Show AK duration in time-like format, not decimal format

AKModel/models.py

@@ -336,6 +336,15 @@ class AKSlot(models.Model):
             return f"{self.ak} @ {self.start_simplified} in {self.room}"
         return f"{self.ak} @ {self.start_simplified}"
 
+    @property
+    def duration_simplified(self):
+        """
+        Display duration of slot in format hours:minutes, e.g. 1.5 -> "1:30"
+        """
+        hours = int(self.duration)
+        minutes = (self.duration * 60) % 60
+        return '%d:%02d' % (hours, minutes)
+
     @property
     def start_simplified(self):
         """

AKSubmission/templates/AKSubmission/ak_detail.html

@@ -185,7 +185,7 @@
         <tbody>
         {% for slot in ak.akslot_set.all %}
             <tr>
-                <td>{{ slot.duration }}</td>
+                <td>{{ slot.duration_simplified }}</td>
                 {% if not ak.event.plan_hidden or user.is_staff %}
                     <td>{{ slot.time_simplified }}</td>
                     <td>