[Feature request] Logout all users / specific user from all device

[lcharette]

See #1112. There's is a valid need to be able to logout a specific user, or all user for that matter, from all logged in devices/browser. It's not as simple as removing the "remember me" token in the persistence table. The PHP session also needs to be voided.

Note that calling logout as proposed in #1112 doesn't work, as a) it will void the current user session (can't work to force logout another user) and b) the session from a second browser won't be invalidated.

This function could be available in the admin panel as a button the root user can use to do it manually, or for security measure when modifying a password as described in #1112.