Fix up navigation on the goa page

We were counting accounts as existing, even if they did
not belong to one of the shown providers, and we were never
setting the page as complete.
Accounts: really pick up data from online accounts

The prepopulate code was only run at the time the page is
constructed, which is before the goa page is shown. Instead,
listen for goa accounts that are added, and update the information.
Add a translator comment

https://bugzilla.gnome.org/show_bug.cgi?id=724179