Add chrony service
Also, do not build and add ntp to the system unless it is enabled.
chrony: properly set rtconutc option, and add a few more options
atop: Add basic config option for /etc/atoprc
Merge pull request #170 from wizeman/atop

atop: Add basic config option for /etc/atoprc
Merge pull request #169 from wizeman/chrony

Add chrony service
gnunet: it was missing extraGroups