ui: allow deleting contest/homework via edit page

packages/ui-default/templates/homework_edit.html

@@ -85,6 +85,11 @@
             <button type="submit" class="rounded primary button">
               {{ _('Update') }}
             </button>
+            {% if tdoc.owner == handler.user._id or handler.user.hasPerm(perm.PERM_EDIT_HOMEWORK) %}
+              <button name="operation" value="delete" type="submit" class="rounded button">
+                {{ _('Delete') }}
+              </button>
+            {% endif %}
           {% else %}
             <button type="submit" class="rounded primary button">
               {{ _('Create') }}