Write systemd unit files for daemons

[Flupsy]

Many modern distros are replacing conventional System V-style init scripts with systemd unit files. We should write them for our daemons so that we have native support for systemd.

I've done this for some services on jessie so I can assist (or just do it).

[sagepe]

Relevant: 663bb16

[gbp]

We support systemd in our install scripts #7591 so this change should be relatively easy now.

[HelenWDTK]

This issue has been automatically closed due to a lack of discussion or resolution for over 12 months.
Should we decide to revisit this issue in the future, it can be reopened.

[sagepe]

I think this has been done via #8024.