sysutils/bacula13-server: New ports for Bacula 13

NOTE: I am unsure of how stable this is. Please proceed with caution.

Also coming in:

* sysutils/bacula13-client
* sysutils/bacula13-docs
* net-mgmt/nagios-check_bacula13

Not present yet: sysutils/bacula13-client-static because of unknown
build issues.