AKScheduling: Enforce room availability constraint for newly placed slots, too

This resolves #111

AKScheduling/templates/admin/AKScheduling/scheduling.html

@@ -184,7 +184,7 @@
         <div class="col-md-2 col-lg-2" id="unscheduled-slots">
             {% for slot in slots_unscheduled %}
                 <div class="unscheduled-slot badge badge-primary" style='background-color: {{ slot.ak.category.color }}'
-                     data-event='{ "title": "{{ slot.ak.short_name }}", "duration": {"hours": "{{ slot.duration|unlocalize }}"}, "description": "{{ slot.ak.details | escapejs }}", "slotID": "{{ slot.pk }}", "backgroundColor": "{{ slot.ak.category.color }}"}' data-details="{{ slot.ak.details }}">{{ slot.ak.short_name }}
+                     data-event='{ "title": "{{ slot.ak.short_name }}", "duration": {"hours": "{{ slot.duration|unlocalize }}"}, "constraint": "roomAvailable", "description": "{{ slot.ak.details | escapejs }}", "slotID": "{{ slot.pk }}", "backgroundColor": "{{ slot.ak.category.color }}"}' data-details="{{ slot.ak.details }}">{{ slot.ak.short_name }}
                     ({{ slot.duration }} h)<br>{{ slot.ak.owners_list }}
                 </div>
             {% endfor %}