Added a new flag 'configure_without_carrier' which will tell
systemd-networkd to configure the device even if no carrier found.

Furthermore the template will accept the absence of ipv{4,6} and
gateway{4,6}.

Note the jinjia comments "{# Keep the line below empty! #}".
If there is no empty line below this comment the templating will fail.
This will result in templating all device configs into a single file.

TODO: Make subnet configurables.
Muckefuck will have a 192.168.1.0/24 ip for communication with the hdmi
switch. Currently all ips for hosts in group "fachschaft" will be added.
So we limit that to the subnet 131.234.0.0/16.