Add description text for logging options.

Some Php applications including Cron scripts may fail because this file is missing from chrooted /etc.

use seperate config for amavis-dkim-config even is the systems uses a monolith config to prevent overwriting the key-config during updates

Removed ubuntu1604.lib.php which is not required anymore.

- Introduced confid in $distver array to separate the config and class for a distribution in the installer.
- Cleaned up the dist detection.