Nice Mail notification on Recharge

[cfstras]

in https://github.com/flipdot/drinks-scanner-display/blob/master/screens/recharge_screen.py
and https://github.com/flipdot/drinks-scanner-display/blob/master/webserver/webserver.py#L86

only when ldap setting contains "instant"

use code from https://github.com/flipdot/drinks-scanner-display/blob/master/users/sync.py#L71