api: export last_update_time in formdata json (#6640)

help/fr/api-get.page

@@ -42,6 +42,7 @@ Le contenu ainsi obtenu est le suivant :
 {
     "id": "newsletter/16",
     "receipt_time": "2013-01-04T13:39:47",
+    "last_update_time": "2013-01-04T13:41:21",
     "fields": {
         "email": "marc@example.net",
         "nom": "L.",

wcs/formdata.py

@@ -480,6 +480,14 @@ class FormData(StorableObject):
 
     concerned_roles = property(get_concerned_roles)
 
+    def get_last_update_time(self):
+        if self.evolution and self.evolution[-1].time:
+            return self.evolution[-1].time
+        else:
+            return self.receipt_time
+
+    last_update_time = property(get_last_update_time)
+
     def anonymise(self):
         for field in self.formdef.fields:
             if field.anonymise:
@@ -510,6 +518,7 @@ class FormData(StorableObject):
                 'name': self.formdef.name,
                 'id': data['display_id']}
         data['receipt_time'] = self.receipt_time
+        data['last_update_time'] = self.last_update_time
         data['url'] = self.get_url()
 
         try: