The controller /event/<event_id>/page/<page> raise exception if page is not existing.
Allow to pass the template reference when user are creating a new page.
Without it, it is impossible for the end user to create a website_event page without
change manually the xml id because the xml id is based on the module from the template.
This fix is retro compatible, because from_template will be ignored until next update
of website. And during update from website, website_event will be updated because it's a
dependance and so the default_page template created.
Jeremy Kersten
ce3f797068