base: implemented language button: - `component.menu` can now be used with a `{% call %}`, allowing extra HTML to be added after in the <nav> element - a language dropdown is shown if more than one translation is available, allowing to change page locale - if javascript is available, only the dropdown is visible, and changing it reload the page with new locale - if javascript is not available, a submit button is display to change the locale

[jinja2: **.html]