Install galileo as a daemon

[Dylan <bob.dybian@gmail.com>]

Hi,
Some users request the possibility to install galileo as a daemon, so
I updated the package to do it.

Since I do not want to run galileo as a daemon for my own use. I
create a new binary package "galileo-daemon" which configure galileo
as a daemon.
This new package installs a systemd service file and a new udev rule
to run galileo as a daemon. This new rule overrides the previous one
(with a higher priority). And finally, it creates a new specific user
to run the daemon.

Since this new package is more sensible than my previous ones, I would
like to have some comments/advises on it [1] before to ask a
sponsorship.

Thank you.

Best regards,
Dylan

[1] https://anonscm.debian.org/git/debian-med/galileo.git/commit/?id=919e32cc9