Provide init (systemD) service for the docker OMV image

[breznak]

It would be nice to have an init service that could handle automatic (re)starts of the image.
As a reference, I can show the systemd service used in docker-openvpn image:
https://github.com/kylemanna/docker-openvpn/blob/master/docs/systemd.md

[ikogan]

Unfortunately, I don't use OMV anymore so it's unlikely I'll have much time to implement this, although a PR would be great.