Refactor `SessionIdleTimeout` in `session_timeout_middleware.py` to redirect to login page when session has timed out.
Add `is_student` in `AuthFlags` class in `facility/middleware.py`.

Refactor SessionIdelTimeout in session_timeout_middleware.py.
1. Remove ellipses in error message.
2. Use `is_student` in `if` condition for authenticated logged in *student* users.
Refactor `test_facility_user_logout_after_interval` method in `TestSessionTimeout` class at `test/distributed.py`.
Test if login url is equal to the redirected url after session timed out.
Merge pull request #2660 from mrpau/hotfix/2320-redirect-to-login-page-when-session-has-timed-out-and-page-is-loaded

Fixed for issue #2320 Redirect to login page when session has timed out and page is loaded