Accept timezone about next-intl

[amannn]

formats is covered by #14. Still need to investigate timeZone. Is timeZone necessary for timestamp numbers as dates or do they have a defined time zone?

[amannn]

Handling the timeZone is indeed interesting. A server request doesn't include this information, therefore ideally we'd use a setting saved in the user profile or otherwise information from GeoIP. Both can not be known by this library, therefore the user should provide this.

See also https://stackoverflow.com/questions/6091804/is-there-another-way-to-get-a-users-time-zone-from-a-httpservletrequest-object/6091881#6091881

[amannn]

On the client side this is different. E.g. when the user provides a time via a date picker for example, we can typically read the timezone of the user and add it to the date. Not sure yet if that affects this library, as during render only timezone-aware dates should be used. In the change handler of a date picker a timezone can be added immediately.