R1:ebd8f3c9874b

Make translation, timezone and pronoun into real settings

Summary:
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.

Test Plan:
- Set settings to unusual values.
- Ran migrations.
- Verified my unusual settings…