[FIX] web_calendar: use local format for week in title of calendar view.

Commit odoo/odoo@9be7a9535ca1c5a9884ef06b7a567bf42ebdce0a changes the week number
computation to match calendar and pivot views.

Now, calendar don't use isoWeek format by default, but the weekNumber from locale(),
So we need to adapt also the format for title.

closes #12068, closes #9629