install dkim on directadmin in exim

[golfreeze]

https://help.directadmin.com/item.php?id=569
Assumes you've got /etc/exim.conf 4.5.x or newer.
Turn it on
#cd /usr/local/directadmin
#./directadmin set dkim 1

Enable it in the exim configs and exim:
cd /usr/local/directadmin/custombuild
#./build update
#./build exim
#./build eximconf

Turn it on required domains
#cd /usr/local/directadmin/scripts
#./dkim_create.sh domain.com