region: Allow setting system-wide formats

https://bugzilla.gnome.org/show_bug.cgi?id=695535
region: Never show "None" for language and formats

If the settings backends fail to give us valid values, show the
current environment instead of "None" since we do know which language
is actually being used.

https://bugzilla.gnome.org/show_bug.cgi?id=695535