The date time picker is not localized

Follow these steps to reproduce:

• enable multilingual and set at least 2 supported locales (e.g. en and ro)
• open /xwiki/bin/edit/Help/Applications/Movies/Meet John Doe?force=1&language=ro
• focus the Release Date property in order to open the date picker

The date picker should be localized:

• name of week days
• name of months
• first day of week should depend on the locale (Monday vs. Sunday)
• tool tips