Use Xautolock+slock instead of XScreenSaver

Improvements over XScreenSaver:
- Respects fullscreen applications, including at least VLC/mplayer <https://unix.stackexchange.com/questions/46973/how-to-create-a-screen-lock-timer-for-awesome-wm>
- Goes straight to black screen when resuming from hibernation <https://unix.stackexchange.com/questions/144591/how-to-properly-lock-desktop-when-hibernating>
- Much smaller (70 KiB vs. 22.38 MiB)
- Much simpler configuration
Add Liberation TTF font

As recommended by <http://archlinux.me/axel668/2012/12/20/10-things-to-do-after-installing-archbang-2012-12/>
Enable NTP daemon
Remove unused `service` commands
More explicit `systemctl` calls
Enable SSH daemon
Tags
Various systemd status calls