The separator went missing when we started adding the popular
languages to the list. Make it come back to separate the user
languages from the popular ones.
Similar to how we format language names, add a variant that
emphasizes the region part of a locale. We show the language
in parentheses as discriminator only where needed.
This just code loads one language at a time in an idle,
to avoid blocking the UI for a long time. The function returns
the id of the sources, so you can just call g_source_remove()
if you don't need the languages anymore (e.g if the user goes
to another panel before the list is fully populated).
https://bugzilla.gnome.org/show_bug.cgi?id=643096
Make more of the code common one, so we can re-use it for
the region panel. Show the user's current locale first, as well
as the list of languages used by other users, followed by a separator.
