list_users / list_roles sync issue

[tinkertoy]

When adding or deleting a user or a role from the sample application "admin" page, the change gets written to the relevant json file when the submit button is clicked, but reloading the admin page alternates between the state prior to the change and the state after the change.

Exposing _refresh() from json_backend.py and calling it upon entry in list_roles and list_users fixes things for me.