[Bug 827645] Add locale column to questions.

This makes the changes needed to the model, and adds the migration. This migration should *not* be run directly on production, because that would likely to Bad Things:tm:. We need to do a dance with the database cluster to get this to work in production, I'll handle that with Sheeri's help. This is, however, perfectly safe to run on our local instances, and for me it only took about a minute.

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