last things and fixes for some of the iSec reported issues

Inlcudes some of the fixes for issues reproted by iSec and the fix for unattended-upgrades that I was working on when iSec started the sec audit. Closes #439, #437, #435, #441 

Also adds
- the facistfirewall setting to torrc file so that the ports could also be restricted in the iptables rules. 
- Example network firewall rules
- xSendFile so that large files can be downloaded
Since adding postfix to the environment, OSSEC doesn't send the email directly to the distant smtp server. It sends it it to root@localhost. Procmail picks up all mail sent to root@loacalhost, encrypts the bodies and then postfix sends the emails to the distant end. The postfix configuration is described here: https://github.com/freedomofpress/securedrop/blob/develop/docs/install.md#configure-postfix with an example for gmail as smtp relay. So that question wasn't doing anything anymore.