Ref T4103. These are currently stored on the user, for historic/performance reasons.

Since I want administrators to be able to set defaults for translations and timezones at a minimum and there's no longer a meaningful performance penalty for moving them off the user record, turn them into real preferences and then nuke the columns.

• Set settings to unusual values.
• Ran migrations.
• Verified my unusual settings survived.
• Created a new user.
• Edited all settings with old and new UIs.
• Reconciled client/server timezone disagreement.