Add expiry dates and individual conditions to gift cards (#1656)

* Add expiry dates and individual conditions to gift cards

* Display refund gift cards with more details and prettier interface

* Allow to set gift card expiry and conditions when cancelling event

* Extend gift card search

* Fix #1565 -- Some gift card filters

* Improve list of gift cards

* Allow to edit gift cards

* Note on validity

src/tests/api/test_giftcards.py

@@ -27,6 +27,8 @@ TEST_GC_RES = {
     "secret": "ABCDEF",
     "value": "23.00",
     "testmode": False,
+    "expires": None,
+    "conditions": None,
     "currency": "EUR"
 }