Don't crash for missing DMI

Some systems don't have DMI devices

Patch from Tony Espy <tony.espy@canonical.com>
Add new rfkill type: NFC

Patch from Tony Espy <tony.espy@canonical.com>
Add NFC to glib and docs
Check glib version for g_type_init()

g_type_init() is deprecated since glib 2.36