Universale Time Format Setting

We have quite a few apps that show the date and it's come to my attention that users want to have different date formats. This can be dependent on your locale where the month should come before the day in some cases and after the day in others, or this can be dependent on how technical you are where some users want to see "Today" and some users want to see "2011-10-29".

Currently, each app either handles this independently with no configuration or handles it's own configuration and what we end up with is a system where it's really hard for a user to simply set how he wants to see the date across the whole OS.

What we need to do is create a universal dconf key that we can all use and that can be set in Switchboard so that we can get really nice date formats for free in our apps and that users can see the format they want consistently in all of our apps.

Of course we do have to have a way to keep certain provisions in showing the date. For example in Marlin it might make sense to show the full modify date down to the second, but in Dexter you only want to see the day, month, and year of a person's birth.

Initially API and GSettings schema can live in granite. Ultimately it should be upstreamed to GLib.
A possible location for this key(s) would be /system/locale

Example Formats:

Today at 5:36 PM
Today at 17:36
December 17th, 2011 at 5:36 PM
17 December, 2011 at 17:36
17-12-2011 at 17:36:03