Log the times when external IP address changes

src/freedombone-utils-network

     echo 'if [[ "$curr_ip" != "$existing_ip" ]]; then' >> $ip_update_script
     echo "  sed -i \"s|EXTERNAL_IPV4_ADDRESS=.*|EXTERNAL_IPV4_ADDRESS=\${curr_ip}|g\" $CONFIGURATION_FILE" >> $ip_update_script
     echo '  iptables-save > /etc/firewall.conf' >> $ip_update_script
+    echo "  echo \"\$(date)\" >> ~/${PROJECT_NAME}-external-ip-changes.txt" >> $ip_update_script
     echo 'fi' >> $ip_update_script
 
     cron_add_mins 10 $ip_update_script