Add item and variation ID to pretixdroid API

src/pretix/plugins/pretixdroid/views.py

@@ -174,7 +174,9 @@ def serialize_op(op):
         'secret': op.secret,
         'order': op.order.code,
         'item': str(op.item),
+        'item_id': op.item_id,
         'variation': str(op.variation) if op.variation else None,
+        'variation_id': op.variation_id,
         'attendee_name': name,
         'redeemed': bool(op.checkin_cnt),
         'paid': op.order.status == Order.STATUS_PAID,