Implement account update method

Allow syncing of all known accounts from PowerDNS, in the same
way that Domain().update() does for domains.

update_accounts.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+
+####################################################################################################################################
+# A CLI Script to update list of accounts. Can be useful for people who want to execute updates from a cronjob
+#
+# Tip:
+# When running from a cron, use flock (you might need to install it) to be sure only one process is running a time. eg:
+# */5 * * * * flock -xn "/tmp/pdns-update-zones.lock" python /var/www/html/apps/poweradmin/update_accounts.py >/dev/null 2>&1
+#
+##############################################################
+
+### Imports
+import sys
+import logging
+
+from powerdnsadmin import create_app
+from powerdnsadmin.models.account import Account
+from powerdnsadmin.models.domain import Domain
+from powerdnsadmin.models.setting import Setting
+
+app = create_app()
+app.logger.setLevel(logging.INFO)
+
+with app.app_context():
+    status = Setting().get('bg_domain_updates')
+
+    ### Check if bg_domain_updates is set to true
+    if not status:
+        app.logger.error('Please turn on "bg_domain_updates" setting to run this job.')
+        sys.exit(1)
+
+    Account().update()
+    Domain().update()