g-s-d has been taking care of this for us but in a very hackish way
that causes dconf writes on every startup and also doesn't handle
dynamic updates to locale1's properties which has become a problem now
that GDM keeps its greeter session running in parallel with users'.
To take care of this properly, this commit introduces a settings
abstraction with both system and session implementations. The session
implementation just wraps access to the existing gsettings while the
system one gets its values from org.freedesktop.locale1's properties.
https://bugzilla.gnome.org/show_bug.cgi?id=746288
4da2862f8f