Allow worldwide region for paid apps WiP (bug 883933)

This turns on the worldwide checkbox in the devhub for paid apps.

It doesn't deal with any functionality wrt to dealing with the worldwide region being enabled and adding a new region - we'll need to tackle that separately - there's already a bug to work out what is needed which is here: https://bugzilla.mozilla.org/show_bug.cgi?id=882798