"remember me" supports parallel login from multiple devices

A new table "user_connections" can now store multiple token for each user.
This allow users to use "remember me" function independently on all their devices.

For people who use [panique/php-login-advanced](https://github.com/panique/php-login-advanced) in production and don't want to force all users to login again....
After installation of my version, you can run the query below :
`INSERT INTO user_connections (user_id, user_rememberme_token, user_login_datetime) (SELECT user_id, user_rememberme_token, now() FROM users WHERE user_rememberme_token IS NOT NULL)`