Built-in notion of user timezone

[ebruchez]

Especially now that we have #7324, we should be able to simply expose a property called, for example user.profile.timezone (name TBD).

This can come from, in order of priority:

• a user profile property provider when available (API to extend and manage configuration properties #7324)
• an external header if possible with embedding (Ability to pass the timezone by header #4724 )
• a global server property
• the server's timezone

Introducing this would at least allow formulas in forms/Form Runner itself to use that property.

See also:

• Option to adjust date/time to JavaScript timezone #7519
• Configurable timezone storage for dateTime #1836

+1 from customer