skeleton: apply locale settings in user shells

Add /etc/profile.d/locale.sh script from Arch Linux to /etc/profile.
This script looks for locale.conf, sources it, and exports the LANG and
LC_* variables.

[Arnout: put in /etc/profile in the skeleton rather than making it
 systemd specific.]

Signed-off-by: Maxim Mikityanskiy <maxtram95@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>