Add a check_apns_tokens manage.py command to flush old tokens

(imported from commit 15dcfaa1967bd749b582882c4a816a457ca6cc12)

zerver/management/commands/check_apns_tokens.py

@@ -0,0 +1,18 @@
+from __future__ import absolute_import
+
+from django.core.management.base import BaseCommand
+from django.conf import settings
+
+from zerver.models import AppleDeviceToken
+
+from zerver.lib.push_notifications import check_apns_feedback
+import logging
+
+class Command(BaseCommand):
+    help = """Checks the Apple Push Notifications Service for any tokens that have been
+              invalidated, and removes them from the database.
+
+    Usage: ./manage.py check_apns_tokens"""
+
+    def handle(self, *args, **options):
+        check_apns_feedback()