Fix nuxeo-date element to take into account locale and/or timezone

When setting the locale to French in the browser, the dates are still displayed with English formatting. We see

 January 30, 1981

instead of

 30 janvier 1981

This bug does not exist with LTS 2019 (Elements v2.4), so I tried to compare the code :

2.4 : https://github.com/nuxeo/nuxeo-ui-elements/blob/maintenance-2.4.x/widgets/nuxeo-date.html has a "timezone" property which is used to format the date

3.0 : https://github.com/nuxeo/nuxeo-ui-elements/blob/master/widgets/nuxeo-date.js does not have a timezone

Maybe it's the root cause of the issue.

Expected behavior: the date is displayed with the standards of the language set in the browser.