nixos/gnome3: add gnome-settings-daemon udev rules (enables bluetooth GUI)

Without this, gnome-settings-daemon will not have write access to
/dev/rfkill, which in turn cause it to advertise no "airplane mode" over
D-Bus, which in turn the bluetooth panel code in gnome-control-center
interprets as "there are no bluetooth dongles" (and the button to turn
on bluetooth is grayed out). The end result that bluetooth operations
cannot be done in the GNOME desktop.

See upstream discussion:

http://lists.usefulinc.com/pipermail/gnome-bluetooth/2016-July/thread.html
http://lists.usefulinc.com/pipermail/gnome-bluetooth/2016-December/thread.html