Add a new script that checks for TU votes ending within the next 48
hours and sends reminder emails to all Trusted Users who did not cast
their votes yet.

The script is designed to be executed as a cron job, such that the check
is performed periodically. Since the script does not remember users it
already sent emails to, the interval should not be chosen too small to
avoid spamming.

Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>