We pretty much only run in systemd environment and I don't see that
changing any time soon. By relying on it, we can reduce some burden.
Remove init script.
Daemonizing is not needed for systemd. Remove code related
daemonization.
- When running in an environment without systemd, the changes are completely
ignored.
- When running under systemd, the patch introduces a systemd native service
file to take advantages of nice feature provided by systemd.
- One of the feature currently taken advantage of is the ability to restart the
service automatically if it ever crashes or exits with error.
- Another feature is that when we wish to kill Plinth all the processes under
the cgroup are killed as well.
