Remove fstab and mtab

These are now managed by systemd
Switch to a generated changelog
Update /etc/issue for Pragmatux 3.0
Use config-package-dev to displace Debian's /etc/issue
Add os-release
Change default hostname from 'ptux' to 'device'
Update motd to work with current initscripts package
Set the default locale to the special locale "POSIX"