Improve display of locked user accounts

The "Failed Logins" column on manage_user_page.php does not immediately
tell the Administrator whether an account is locked or not (unless they
remember the value of $g_max_failed_login_count).

If the login count >= max_failed_login_count, display a padlock icon
next to the number.

Column has been moved left, after "Protected".

Fixes 0036840