bring back remember-me

bring back remember-me
* try to reuse the old session token for remember me login
* decrypt/encrypt token password and set the session id accordingly
* create remember-me cookies only if checkbox is checked and 2fa solved
* adjust db token cleanup to store remembered tokens longer
* adjust unit tests

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>