When the daemon was started as root (f.e. vi systemd unit),
some users had to issue the "xhost +" command for some programms
(f.e. FreeCad).
With this support, spacenavd can started as root and switch on runtime
to an other uid / gid. So a "xhost +" command isn't longer neccessary
when proper uid or gid settings are used (f.e. the "standard" user of
the system).
With the invoked uid / gid spacenavd stills open the pid and socket file
and also use it for device dection.
Also implemented user/group configfile setting.
Thomas Martens