Move TimeZoneProperty to user preferences page

[mawinter69]

The TimeZoneProperty is currently on the account settings page. I think it betters fits on the Preferences page. Alternatively it could also be on the Appearance page thought that setting could also be used by plugins for other non UI things.

Testing done

Tested that property is on the right page and still works.

Proposed changelog entries

• Move the user time zone configuration to the user preferences page.

Proposed changelog category

/label rfe,web-ui

Proposed upgrade guidelines

N/A

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Desired reviewers

N/A

Before the changes are marked as ready-for-merge:

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• There are at least two (2) approvals for the pull request and no outstanding requests for change.
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[daniel-beck]

I was looking for this recently and was confused why it wasn't in one of the more "obvious" locations, so +1 from me.

[timja]

Preferences makes sense, it doesn't belong on appearance.

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/label ready-for-merge

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This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.

Thanks!

[A1exKH]

LGTM.